Contrary to 35 mm projectors, digital cinema projectors are able to project content from all kinds of sources on the screen. For cinema owners, this represents a great potential for additional revenue. It’s now possible to give cinema audiences access to all kinds of exciting new content on the big screen: opera or live concerts by satellite, video game parties or host a conference by connecting the speaker´s laptop to the projector.

These ´alternative projections´, that are often seen as added value that come with the system for free, are not necessarily obvious and can be quite hazardous to handle. Digital cinema projectors were primarily designed to project images and sounds of feature films from the digital cinema server. Connecting other devices - that generally means external video sources - may hold some surprises: bad aspect ratio, artifacts, audio noise, ...

In several chapters Cineserver will give you explanations and tips about how to get alternative content screenings running smoothly with the different kinds of video players. Firstly, we will discuss several aspects of video:

• the basic principles of video
• the different video connectors
• connecting a video player directly to the projector
• the benefits of using an intermediate device: the video scaler

Following chapters will discuss how to connect audio sources, we´ll discuss how to connect laptops and different consumer and professional video players and will have a separate section about satellite receivers.

The inputs of a digital cinema projector

Several inputs are available on the input panel of d-cinema projectors to connect video players. The main ones are the two HD-SDI inputs that securely connect the cinema server to the digital cinema projector. This connection is known as dual link HD-SDI and provides a nominal 2.970 Gbit/s connection. Digital cinema projectors commonly also have two DVI (older projectors) or HDMI inputs (some more modern models) on the input panel. These connectors can be used by the projectionist to plug in a DVD player, a laptop or a satellite receiver, most often using an intermediate device.

DVI inputs A and B on a NEC 2500 projector. On some recent projectors one can find one or two HDMI inputs instead. >>>

Doremi's Integrated Media Block, here on a Barco projector. It has an HDMI input to easily plug in HD video players lik >>>

DVD-player, Blu-ray and HDCAM, connected to a Christie Cine-IPM scaler.

The larger the screen, the more faults will be visible ...

On the big screen, the image’s faults are obviously going to be more noticeable than on a small television screen. Therefore, if available, a High Definition image is highly preferred for what is often called 'alternative content'.

In order to understand the different signals that can (directly or indirectly) be plugged into a digital cinema projector, we first need to understand the terminology that describes these various signals. The first major distinction that we can make is between analogue and digital video signals.

In analogue video signals, the information is conveyed by continuously varying electric signals, quantities being represented by levels or voltages. Analogue is typical of nature and the human senses. Analogue video signals are prone to interference and distortion during transmission.

Digital information is conveyed by discrete states (on/off) and its quantities are represented by numbers. Digital information is fundamental to Information Technology and is more robust for storage and transmission than analogue signals. Digital technology is often described as 'bits and bytes', without the person using really understanding what that means.

A bit is a single digital state (on / off).

• One bit can represent values from 0 - 1
• Two bits can represent values from 0 - 3
• Three bits can represent values from 0 - 7
• 16 bits can represent values from 0 - 65535

A byte is a group of eight bits and it can represent values from 0 - 255. A byte is typically used to hold a single printable character and is commonly used as a basic measurement for storage. In digital video signals, these 'bits and bytes' are used to form an image. This image is often described in pixels or resolution.

Pixels are picture elements and represent the smallest part of a digital image that can be individually controlled. An image is a rectangular block of pixels. The resolution of a digital image is the number of pixels contained in an image. It is usually expressed as Horizontal Pixels x Vertical Pixels, for example 1920 x 1080 (HDTV), 1024 x 768 (PC XGA). A pixel doesn’t have a specific size; a large screen can contain as many pixels as a small screen. Every pixel is described by 4 bytes (32 bits) in order to be able to represent all colours ranging from black to white.

Now that we have an image, in cinema we need to produce a moving image. These are the terms used to describe the moving image.

A frame (of a digital image) can be compared to a digital photograph in time, containing all pixels required to reproduce the image.

The frame rate is the number of frames displayed in each second. For example: film has a frame rate of 24 fps, TV is 25 fps, US TV is 29.97 fps. The abbreviation fps means frames per second.

An important term that one also comes across in digital cinema is colour space. This describes the way in which the colour of the image is described, also giving limitations as to the range of the colour. More formally it is called Colour Specification System.

Coulour space is the way in which colour information is represented for storage, transmission and reproduction of digital images. There are several types in common use for images, for example R'G'B', Y'Pr’Pb (Rec. 709) and X'Y'Z' (the standard colour space for digital cinema). An image will only be reproduced correctly if it is decoded in the colour space in which it was encoded.

Interlaced is a term that we find in tv's, but as a remnant it is still found in professional video equipment. It is a technique of improving the picture quality of a video signal, without consuming extra bandwidth. Historically, in television the image was portrayed in 2 fields, one showing half the image and the second field the second half, generally in odd and even lines. The switching happened so fast, that the human eye didn't even notice and just saw the one image. You can say that half the information was processed at twice the speed. The reason for using interlacing, was that the original bandwidth was limited and by processing only half the image at a time, the quality could be improved.

A field (of digital image) is a portion of a frame in an interlaced image. It usually holds half of the vertical pixels (lines), typically all odd or all even numbered lines.

Progressive Modern video images are 'progressive', showing one frame after an other. We also find this back in video terminology: for instance 1080i refers to an image which is high definition and interlaced, where as 1080p tells us that the images are progressive. When interlaced video is shown using a video scaler, we have to de-interlace the image to improve the quality. This might be necessary as interlaced video is not very good at showing fast moving images, as these show fuzzy edges to the moving objects, instead of straight lines. The difference between interlaced and progressive, combined with multiple frame rates, can provide particular problems when transferring film to video.

Video players (DVD, Blu-ray, game consoles ...) can have different types of outputs / connectors. The projectionist who wants to connect one of these drives to its d-cinema projector, must choose the connectors that will enable him to get the best picture quality and the best sound. There are two types of connectors of peripheral equipment: digital and analogue.

Digital outputs

Digital outputs are generally the best option when connecting a video signal to a digital cinema projector. During transport from the source to the projector, analogue signals can generally degrade for instance due to bad connectors or long cables, causing interference, drop of quality etc. A digital link virtually provides a guarantee that the signal emitted by the player will experience very little degradation during transport to the projector.

Analogue outputs (in the white circle) and digital outputs (in the red circle) on a Sony Blu-ray player

SONY's SRW5000 HDCAM player has 2 HD SDI outputs on its rear panel.

The HD-SDI interface can carry a high-definition signal. It requires a high quality coaxial cable; the data rate that passes through it can reach 1.485 Gbit/s and has a high resistance to interference signals. The BNC connector characterizing this interface ensures a solid connection with little risk of a loose contact.

A characteristic of the HD-SDI outputs is that it transports only image, and no sound, which in cinema is generally not a problem as we use separate systems for video and audio. However, there is a technical solution for transporting the audio signal with the video through HD-SDI by adding an extra box called ‘SDI/AES De-Embedder’. When using HD-SDI a more common way to handle the sound is by using XLR connectors (reserved for professionals) which then handles transportation of the sound to the processor.

DVI (Digital Video Interface) outputs.
Designed to carry uncompressed video images of a player to a projector, the DVI connection is a high quality connection, boasting a high data rate that can carry high definition signals (HD). Like HD-SDI, DVI transports only images, not sound.

The DVI connector has been used a lot in the past on computers, video projectors and DVD players. Nowadays HDMI, which can handle both video AND audio has often taken the place of DVI, which limits the number of cables required. However, an advantage of DVI over HDMI - especially in professional use -is that the connector is much more robust, as it is fitted with screws, guaranteeing a secure connection.

There are 3 types of DVI connectors, that can be recognised by the number of pins in the connector:

• DVI-D (DVI-Digital) : transports only digital signals

• DVI-A (DVI-Analog) : transports only analog signals

• DVI-I (DVI-Integrated) : can transport digital and analog signals, but not both at the same time

DVI is partially compatible with HDMI in digital mode (DVI-D), and with VGA in analogue mode (DVI-A or DVI-I).

DVI cable with connectors.

HDMI cable.

The success of HDMI originates in the fact that it carries both image and sound signals, as opposed to DVI which only carries image. This is a great benefit for consumers because all they need is one cable for connecting peripherals to their television screens. But HDMI does not simplify the job of the projectionist, because in cinemas video and audio signals are treated separately: the first in the projector and the latter in the sound processor.

There are many successive versions of HDMI (versions 1.0, 1.1, 1.2, 1.3, 1.4), all with different characteristics, becoming more advanced with each version number. Today, the most common HDMI connector is 1.3 which features a maximum data rate of 10.2 Gbits p/s maximum. The upcoming version 1.4 will be able to handle 3D content in HD (1080P) and 4K content (4096 x 2160 pixels). HDMI and DVI are compatible with each other, so converters can be used to connect HDMI video sources to projectors with DVI connectors and vice versa.

HDMI is compatible with the HDCP copy protection standard, which protects high definition (consumer) content like Blu-ray discs against unlawful copying. This can present problems in cinemas, as many of the first generation of d-cinema projectors did not support the HDCP-standard, so HD-content cannot be played on their digital external inputs. In this case, an analogue connection will do the trick, but we’ll return to this issue later on.

Analogue outputs

The use of an analogue interface for connecting a device to a d-cinema projector may not be an optimal solution since the signal carried between the two devices may deteriorate during transport, especially if the cable used is not of premium quality. But that does not mean that one should systematically exclude the use of this type of interface.

Please note: unlike HDMI, and with the exception of the SCART connector that is not used in cinema, all analogue connections only transport images. It is therefore imperative to use other (extra) cables for sound.

RGBHV.
RGBHV uses five cables to transport a video signal and is generally only found on professional video equipment. Three cables are used to transport the primary colours (Red, Green, Blue) and the two remaining ones are used for the horizontal and vertical synchronisation of the image.

RGBHV can be used to transport high definition signals between a player and the projector. As it produces a high quality signal, it can replace digital signals if necessary.

RGBHV cable.

Component video output on a Blu-ray disc player.

There are different types of RGB / component video, but the term generally refers to YPbPr video with sync on luma. The ability to transfer video using the RGB interface stops at the 1080i standard (interlaced images of resolution 1920 x 1080).

VGA (Video Graphics Array).
This connector is a version of the RGB analogue video component standard, that is generally found on computers, laptops and computer monitors. As it is so common on most computers, in cinemas this connector is generally favoured for simple PowerPoint presentations, as the quality is considered good enough to display these images.

The connection between the source and the projector (or scaler) is generally secured with two screws. However, there are VGA outputs on the market, generally found on small laptops, that got rid of the screws in order to save space. When used for presentations, these connections should be secured using Gaffa tape.

S-video.
When using an S-video interface (max 720 x 576 pixels), the image signal passes from the player to the projector via a single cable. Within this, the luminance and chrominance are separated through separate conductors which only partially minimizes quality loss. However, this does not prevent the occurrence of interference, especially considering that the vast majority of S-video cables are of poor quality. This connector is therefore to be avoided for the large screen.

VGA cable.

S-video connector (here in high quality).

Cinch (RCA) cable. 

Digital projectors have been primarily designed to project images of 2K and 4K resolution from a digital cinema server. However, as we have seen in previous chapters, their DVI or HDMI inputs makes it possible to hook up external video players.

This might appear simply ‘plug and play’, but in reality we can encounter our fair share of technical issues. While a digital cinema projector is capable of processing video from external sources, this is generally only possible in a specific video format, a particular frame rate and in a single specific colour space.

This is one of the the main challenges for dealing with alternative content: there is a multitude of media formats and frame rates out there. Of course there are tools which can be used to identify problems, in order to get prepared for this kind of content. This is particularly true for the workbench that offers technicians the opportunity to view content on a monitor, before it is projected on the big screen.

This set-up allows pre-visualization, to establish the precise technical details of the program: image format, frame r >>>

A monitor in the top right of the photo: a very useful tool for projectionists.

But the use of a monitor does not guarantee the success of a screening. A video can play perfectly on a monitor and not show up at all on the screen. To be absolutely certain that the show will go smoothly, the projectionist must connect and test its source material under the exact conditions of its future screening (same media, same connection). For this, he / she has two options:

• Connect the source directly via DVI or HDMI to the projector.

• Use a video scaler between the source and the projector.

In modern projectors - the DLP Cinema series 2 - most content in 1080 or 720 resolution can be displayed directly without any problem. In order to connect video signals directly to older projectors, the projectionist or installer must first create one or several macros specifically dedicated to external sources. Both external inputs A and B can handle alternative content, but it is possible to significantly expand these. For example, that is the case for the list of macros available on the sidebar of this Barco DP2K20.

The list of macros available on the sidebar of a Barco DP2K20.

Creating a macro via the dedicated menu: here, the projectionist chooses colorimetry (8, 10 or 12 bits per colour).

• Colour space: RGB, XYZ...

• Resolution: HDTV, XGA ... different types are stored in the projector

• Frame rate: 24 frames per second for film, 25 fps for European television, 29.97 fps for US television...

• Optical adjustments: the format of the source should match the projection

Each video source has its own specific characteristics. For example, an HD CAM SR player can work in a full colormetric area, which is not the case for most satellite receivers that are used to distribute live content. Blu-ray players run at 24 frames per second like digital cinema servers or 35 mm projectors, while a European DVD player plays movies at 25 frames per second. This may seem trivial on a data sheet, but can lead to serious flaws, especially on the big screen (jerks, abnormal colors etc).

Once everything is perfectly set up, the projectionist can directly connect the video source to the projector. With professional equipment, the player can be connected using the HD SDI input SMPTE 292 IN of the projector, as is the case in this screening room:

The HD SDI cables of the Doremi server were temporarily disconnected, to make room for the HD SDI of an HDCAM player.>>

Sony 550 Blu-ray player directly connected to a Christie projector.

DVI / HDMI adapter.

In the list of macros on this Barco DP 2000, we find several dedicated to alternative content.

To people used to working with a video beamer in the office or even in cinema environments, a video scaler (sometimes simply called scaler, or even 'multimedia box’) is a new and strange device. Most beamers don't require a video scaler; external video sources like Blu-ray players or computers can simply be hooked up to the beamer, without going through an intermediate device.

A digital cinema projector however was initially really only designed to play feature films from the server, not project external video signals. Only the recent ‘series 2’ projectors have been designed with this in mind.

What is the precise function of the scaler?

The Barco ASC-2048 scaler connected to a Barco DP2K20 projector.

• The projectionist works 'blind' with every new source. What is the frame rate? Which resolution is it? What is the colour space? Only a test screening can help to find out these parameters and that is not always without problems, especially when time is limited.
• Some video sources are only equipped with analogue outputs (entry level notebooks, some game consoles, legacy DVD players...) and therefore cannot be directly connected to d-cinema projectors, as they are only equipped with digital inputs.
• D-cinema projectors have a limited number of inputs and a direct connection is impractical when it comes to juggling multiple video sources (for example a conference alternating projection of a PowerPoint from a computer and images from a DVD player).
• In the case of a direct connection between source and projector, you do not have image enhancement options at your convenience like those included in most scalers. This includes scaling to the resolution of 2K, conversion of interlaced signals to progressive (better fluidity and sharpness of images).

For all these issues, the scaler has solutions. This is why it often plays an important role in managing alternative content. The number of video scalers that can be found in a digital cinema vary greatly. Some cinemas have one scaler per installation, while other cinema chains don’t supply their cinemas with any, as they just want to use their digital cinema installation to play feature films. In the case of the new series 2 projectors, which can handle external video signals, this can be understood. However, it is better to have at least one video scaler in your cinema, that can be connected to all d-cinema installations, for maximum flexibility.

The scaler: a tool that identifies and converts all types of video sources

We have seen that the d-cinema projector does not naturally and spontaneously all video formats. When using direct connections, we must create a specific macro which can be a tedious process when it comes to using a very specific video source. A scaler will play the role of an intermediary that will convert the video source into a readable format for the digital projector.

Although it is possible to directly connect a video source to the digital cinema projector, a scaler is useful because it offers multiple inputs, and the video signal doesn't have to be fine-tuned, or macros to be made in the projector, for the projector to be able to handle the signal. Therefore, it’s easier for the projectionist to make this connection using a scaler. In addition, the scaler accepts a large range of signals (analogue or digital) from all kinds of sources : DVD, laptop, Blu-ray, HD CAM SR player... The input resolution generally ranges from VGA (640 x 480 pixels) to High Definition (1920 x 1080 pixels).

For instance: the Barco ASC-2048 recognizes the signal from external sources and, after processing, routes it to the digital projector in the best possible quality. This includes if necessary an analog - digital conversion and increased resolution. The integrated display gives technical information about the type of input of the source, like in this case a DVD player:

The integrated display gives technical information on the source’s type of input, like in this case a DVD player.

Staying with the example of the DVD, we see that the resolution is increased from 720 x 575 pixels to 2048 x 1080.

A device to connect multiple players to the projector

With at best two DVI or HDMI inputs, the d-cinema projector has no analogue input, which is naturally a problem when we are trying to hook up sources without a digital output. To be universal and user friendly, the scaler has many inputs. Although there are many different makes of scalers, with different characteristics, generally the inputs on offer are:

• HD-SDI: only for professional equipment like HD CAM, Betacam, camera’s...
• DVI: mostly for computers, Blu-ray, DVD player, games console (with an DVI / HDMI adapter).
• VGA: mostly for (laptop) computers.
• RGB: DVD player, Blu-ray, game consoles (for instance when the projector doesn’t support HDCP copy protection)..
• S-video: for low cost or legacy DVD-players.
• Cinch (composite): rarely used in cinema, although it can be useful for connecting a separate preview monitor, if the scaler supports dual (HD and SD) outputs.

The choice of the connection has a huge impact on the quality of the image on the screen. To get the best possible quality, the projectionist has to choose wisely which type of connection to use. Whenever possible, it's best to work with a digital connection and a high quality cable. If there are no digital outputs available on the player, RGB or VGA should be preferred to S-video and cinch cables.

The output interface that sends the signals to the d-cinema projector on professional scalers is generally DVI. For example, this is the output of Barco’s DCS-200.
Both DVI outputs of the Barco DCS-200 (circled in red).

Christie’s Cine-IPM in Biarritz Elysées (France): the projectionist can plug and play many sources.

Both DVI outputs of the Barco DCS-200 (circled in red).

To optimize images, this NEC scaler uses a chip known for its effectiveness: the Realta processor.

A device that optimises the image quality

The scalers used in cinemas convert video signals from different types of video players into 2K (the standard for the vast majority of d-cinema projectors installed today). The principle of this conversion is called upscaling: it involves creating intermediate pixels between the pixels of the source, to increase the image resolution.

This method does not allow the creation of true 2K images, as a blowup to 70mm of a 35mm source does not render the true quality of a 70mm image. But the process of upscaling, using professional equipment, provides an image quality suitable for projecting content on the big screen. Without being miraculous, it can be a great help, especially with sources such as DVD or PowerPoint presentations that are not originally meant to be used on the cinema screen.

An easy way to switch between sources...

The majority of scalers manage a wide range of image formats and video players. Naturally, performance and functionality depends on the model chosen. Scalers are equipped with multiple interfaces to connect them to all sorts of devices: HD-SDI, DVI, VGA, S-video, Cinch. They support all image resolutions, from the lowest (640 x 480 pixels) to the highest (1920 x 1080, awaiting 4 K).

In addition, scalers also compensate the technological limits of d-cinema projectors, including their inability to handle interlaced signals (rows of even and odd pixels that are not displayed at the same time). Effectively, they convert interlaced signals into progressive (even and odd lines are displayed as one frame, for a sharper image).

...or to manage multiple image formats

In addition, the scaler is able to handle several signals at the same time. For the projectionist this can be very useful, for instance in a rental situation where the customer wants to show content from several sources during a presentation. For example, he might want to show a PowerPoint presentation, mixed with some videos played on a Blu-ray player. Without a scaler, the projectionist has to plug and unplug the player each time that he needs to switch between the sources. This takes time and is error prone, with the risk that the projector needs to reset each time, causing ugly blue screens on the cinema screen. With a scaler, it suffices to activate the right source at each change in the control panel of the scaler.

For example, with the Christie Cine-IPM 2K, the projectionist can plug five sources at the same time to the main inputs.

1. RGBHV.
2. DVI.
3. SDI.
4. Cinch.
5. S-video.

Here, at an event, the RGB input (DVD player) and SDI (HD CAM player) are used.

Remote control of the Christie Cine-IPM 2K.

To switch between the sources connected to the Christie Cine-IPM, the projectionist can use a remote control. An additional advantage of some remote controls is that it can also be connected to the scaler via a cable, using a mini jack connection. This has two advantages. Firstly the connection is more secure than with a wireless connection. And secondly, a long cable can be connected, so the scaler can be operated from the auditorium itself, giving more visual control over the image than when operated from behind the glass of the projection booth.

Scalers from professional video brands like Folsom and Kramer don't come with remote controls, but can be operated and configured using buttons on the front of the equipment. This is generally regarded as a more professional approach than utilizing a remote control, as that can get lost.

Front panel of the Barco DCS-200: the projectionist can switch from one source to another via the illuminated buttons that control each input.

Front panel of the Barco DCS-200: the projectionist can switch from one source to another via the illuminated buttons >>>

Summary of the different resolutions.

The various settings that can be tweaked with a video scaler

Using the video scaler, the projectionist can modify a great number of characteristics of the image. These include:

• The aspect ratio: scalers are used to change the aspect ratio to for instance 4/3, 16/9 or 5/4. The 16/9 format (ratio 1:1.77) is often used on dvd’s and Blu-ray.
• The frequency (refreshing rate) of the image (50 Hz, 60 Hz...).
• The colour space (RGB, SMPTE...).

However, the quality of a video signal is dependant upon multiple factors, like the quality of the original capturing device, the quality of the transmission or storage device and the quality of the display device, in this case the projector. The video signal itself has certain characteristics that are used to describe the image:

• Timing (Sync)
• Brightness (Luma)
• Colour (Chroma)

To control the image quality, most imaging devices have the following picture controls:

• Brightness, or formally: Black level. This offsets the brightness of the whole tonal range of the image. It is most noticeable on dark areas. The brightness should be adjusted so black is only just black. If it is set too low, the image loses detail in the shadows. If it is set too high, the image loses detail in the highlights.
• Contrast, or formally: Video Gain. It adjusts the brightness of light tones in the image. It has most effect on bright areas. The contrast should be adjusted so white is only just white. If it is set too low the image looks 'flat', if set too high it loses detail in the highlights.
• Gamma, or formally: Gamma Correction. This Adjusts the shape of transfer function. It has most effect on the dark and mid tones. Adjustment is rarely required for typical content.
• Colour, also known as Colour Gain or Saturation. This adjusts the amount of colour. It should be adjusted for a natural appearance.
• Hue. This applies to NTSC content only. It adjusts colour shades and can be adjusted to get realistic skin tones.

Some scalers offer the possibility to zoom in on a part of the source image, or exactly the opposite: to enlarge the picture so as to fill the entire screen. Some can also produce a split screen, showing pictures from 2 (or more) different sources, which can then fill the entire CinemaScope screen.

Summing up of the different resolutions:

• SD = 720 x 576 pixels.
• HD ready = 1280 x 720 pixels.
• Full HD = 1920 x 1080 pixels.
• 2K Digital Cinema = 2048 x 1080 pixels.

When it comes to framing, some scalers provide functions like ‘Zoom’ and ‘Pan’ that select a significant portion of the image by zooming it, or trimming other parts. Nevertheless, these operations can also damage the quality of the image, so they have to be done with caution.

However, these options offered by the scaler go against the principles of cinema professionals, who as a rule usually show images the way that the authors have designed them. Historically, projectionists try to respect the framing of films and also specific technical matters, like the minimum level of light and will only adjust the focus and the audio volume. This is not always the norm in the video world, where people won’t hesitate to modify some technical matters to fit specific local situation. But they are therefore also better trained to judge the image quality then cinema people.

Therefore, cinema people aren't used to judging the image quality as people coming from the video world are used to. Therefore, there is a lot to be learnt about this new part of the cinema business.

The different scalers on the market

Video scalers are available from multiple vendors, ranging from expensive models from high end video brands, via mid price scalers from digital cinema manufacturers, all the way down to down right cheap ( € 1000) models from home cinema manufacturers. Naturally the more expensive models have a larger array of connectors, which are also generally directed more towards professional users. But for relatively low prices, there are already fine products like the SP-SOT 2 which uses a HQV chip (very high quality video processing) and various connectors:

A home theater product that could find its place in the projection booth.

A scaler with front panel inputs allows for easier connections.

A scaler with front panel inputs allows for easier connections. Other flaws for professional use: the lack of a control panel that summarizes all essential information (the projectionist must be content here with a summary) and an SDI connection. Some scalers might also have a secondary (low res) output, on which the projectionist can see the menu and control the scaler. However, it is best if only this low res output displays the on screen menu, to avoid the accidental display of a menu during a projection.

In order to connect alternative content signals to a digital cinema system, besides connecting video signals, we also need to hook up the audio. Before we are able to do this, we first need to understand the basics of audio. There are 2 types of audio: analogue and digital audio.

Analogue audio is conveyed by varying voltage and frequency. In consumer electronics this voltage can be up to 3 volts. The connector is usually an RCA (phono) connection for a single channel and a stereo (mini) jack plug for 2 channels, which are both unbalanced. In professional equipment the voltage can be up to 12 volts, the connector is usually an XLR connector for a single channel and it can be either balanced or unbalanced.

It is important to understand the principles of unbalanced & balanced audio connections and of a ground loop, as these can be the cause of nasty buzzes and hums in sound.

An unbalanced connection has one wire for signal and a ground (earth) for the return. It connects the grounds of source and destination equipment together. Therefore it can result in an audible buzz due to a 'ground loop'. An unbalanced connection is also more prone to interference pickup in the cable.

A balanced connection uses two wires for the signal (+/-) and uses ground only for cable screening (shield). These connections are unlikely to suffer from ground loop buzz and are resistant to noise pickup in the cable. Where possible balanced sources should be connected to balanced inputs.

One should always use transformers to connect balanced sources to unbalanced inputs, as due to the coils in the transformer there will be no direct connection between the two grounds. The same is true when connecting unbalanced sources to balanced inputs.

A ground loop appears when a (generally unwanted) current runs through a system that connects two points that are supposed to be at the same potential (often ground) but are really at different potentials. Ground loops can cause audible hums and buzzes to appear in audio signals.

Digital audio is conveyed by a serial bit stream and supports 2-8 channels on a single connection.

On consumer equipment the signal may the stereo PCM or 5.1 using AC3 encoding. The connections can be either S/PDIF on an RCA connection using a coaxial cable or optical on a TOSLINK connection using a fibre optic cable.

Professional equipment always uses two channels per connection. The connections can be an AES3 signal on either XLR or BNC plugs.

In digital audio there are some parameters that one should be familiar with.

• Bit depth governs the signal/noise ratio. More bits means a better signal to noise ratio. Common examples of bit depth include 16, 20 and 24 bits; CD audio is 16 bits.
• The sample rate affects the frequency response: faster sampling is best. Common examples of sample rate include 44.1, 48 and 96 kHz. CD audio is 44.1 kHz, DVD is 48 kHz.

Audio matrixing is a technology where a finite number of discrete audio channels (e.g. 2) are decoded into a larger number of channels on play back (e.g. 5). The channels are generally, but not always, arranged for transmission or recording by an encoder, and decoded for playback by a decoder.

For example: consumer VCR's usually support only two channel audio. Dolby Prologic can matrix four channels into two. These four channels are Left, Centre, Right and Surround (abbreviated as LCRS). Audio matrixing can be applied to either analogue or digital audio. The matrixed channels are abbreviated to LtRt. This technique is similar to film's Dolby Surround ( Dolby Spectral Recording or 'SR').

Audio matrixing can be used on unmatrixed stereo channels, but this may result in strange surround effects. In general it should only be used if content was mastered for Prologic.

Audio encoding

Dolby AC3 (similar to film's Dolby SRD) & DTS can encode six channels (5.1) into two via digital interfaces (S/PDIF or TOSLink). The channels are called Left, Centre, Right, Left Surround, Right Surround and LFE (= Low Frequency Effect, more frequently called subwoofer). These audio encodings are commonly used on dvd, Blu-ray and satellite content. Decoders can automatically detect coded signals, but on audio/video equipment the correct source generally needs to be selected.

Dolby-E is a broadcasting standard typically used in TV studios. It can encode up to eight channels into two. Dolby E only applies to Pro digital interfaces (AES3) and requires compatible VCR's. A Dolby-E decoder automatically detects coded signals.

The following audio formats exist:

• Mono (1.0) - common with archive content and home video. Generally features the same signal on both left and right channels.
• Stereo (2.0 / LR) - Typical of most standard definition content on video tape.
• Prologic (4.0 / LtRt) - Usually only on standard definition video tape.
• AC3 (5.1) - Common on DVD content and PC's.
• Dolby-E - Found only on professional video tape formats (like DigiBeta).
• Discrete Multichannel - Only on HD video tape or SD / HD servers.

Audio connectors

The main audio connectors that exist are:

Analogue:

• Consumer: RCA (phono), 3,5 mm or 1/4" Jack (jack or mini jack)
• Professional: 3-pin XLR (output is male)
• Cinema processor: 25-pin D (Dolby standard)
• Multichannel: 25-pin D (various standards)

Digital:

• Consumer: RCA (phono) or optical (TOSLink)
• Professional: 3-pin XLR or BNC
• Multichannel: 25-pin D (various standards)

Audio format conversion

To interface to the cinema processor, we can come across the following issues

• Digital to analogue conversion. This is required for SP/DIF, Optical and AES3 connections. The way to do this will be discussed in later chapters.
• Multichannel decoding. Prologic is usually built into cinema processors, but an external decoder is required for AC-3, DTS & Dolby-E.
• Audio delay is required to compensate for image processing in the digital projector (2 frames) and video scaler (1-2 frames).
• Switching capability. This is necessary for the selection of sources and film / digital changeover (if required).

A professional converter: the Rane BB 22 Balance Buddy

Trouble shooting

Hum & buzz are usually caused by grounding problems.

• Grounds of sound rack and projector should be tied through the player.

When possible, use balanced connections.

• Break grounds between player and sound interfaces.
• Ground sound interface equipment to the sound rack.

If the equipment is unbalanced, use balancing aids.

• Good quality, line-level transformers
• Electronic consumer/professional converters, like the ART CleanBOX or Rane Balance Buddy.

Remember that unbalanced and balanced equipment are essentially NOT compatible. The only correct and therefore best way to interconnect is by means of transformers. The Rane BB22 also converts the audio level at the same time. The unit can be used in both directions (with aid of gender changing cables for the XLR side).

Originally, the sound processors used in cinema projection booths were designed to handle only the sound from 35mm prints. To decode each sound format (Dolby A, SR, SRD... ), the processor is equipped with a set of electronic cards which are the heart of the equipment.

In addition to the sound processor, the rack of the projection booth usually also contains:

• A small monitor speaker that is used to hear the sound coming from the processor, and allows the projectionist to check it without necessarily physically going into the auditorium. Often the different audio channels can be selected and listened to separately of the rest.
• Amplifiers: they amplify the sound from the processor on each channel (front left, center, front right, left surround etc...).
• A DTS processor (optional; only in auditoriums that are equipped with this sound system). This decodes the DTS audio track that is stored on a CD-ROM ( triggered by the DTS reader reading the DTS track on 35mm film) and sends it to the main audio processor.

Left: the interior of a Dolby CP500 processor.Right: the rear panel of a Dolby CP650 unit with the XLR input (red >>>

Sound equipment rack with amplifiers and Dolby CP650 processor.

Some cinemas also equip their audio racks with a small patch panel, to connect external sound equipment. However, this generally only involves a limited number of inputs, like RCA and XLR. When using these inputs with a balanced source, one should generally favour the XLR input, as that is a balanced input and has superior specifications.

As 35mm projectors are not able to play anything other than 35mm film, until recently the sound processor companies understandably never showed any real interest in compatibility with alternative audio formats.

However, nowadays exhibitors want to hook up their satellite receiver, game console or Blu-ray player to the d-cinema projector. The ´consumer´ audio outputs of these kinds of equipment are incompatible with professional audio equipment like a cinema audio processor.

Recent sound processors like the Dolby CP650 - the most modern sound processor until the arrival of digital cinema - are already more advanced than their predecessors, because they can process multiple sound formats like Dolby Digital or Dolby Prologic, to name but a few. This is particularly useful because Dolby Digital is a format commonly used on dvd, Blu-ray, or satellite broadcasts.

But even with this kind of equipment, it remains problematic to handle 'alternative content', because the CP650 offers only three inputs for external audio sources:

• One XLR input to plug in a microphone.
• Two RCA connections called "NONSYNC" (for playing background music in the auditorium).
• A 25-pin DIN input called "6 Channels Audio input" (traditionally used to connect the DTS sound processor).

These inputs are not suitable to connect consumer equipment. Alternatively, some video scalers can handle both video and audio. Unfortunately the audio output of these scalers can generally not be directly connected to the cinema's sound processor.

Faced with these new requirements made possible by digital cinema, manufacturers like Dolby, DTS (now called Datasat) and QSC have launched processors specially designed for digital cinema. These 'digital cinema sound processors' are not as complex and thus cheaper than traditional cinema audio processors. However, they are generally equipped with multiple audio inputs, adapted to connected the audio connectors used in alternative content.

The back of a Datasat AP20 processor. It offers a wide range of inputs to manage alternative content.

Dolby CP500 processor and DMA8Plus at the Biarritz Elysées in France.

Yet despite these new features, most cinema owners won't seek to acquire a new sound processor when switching to digital cinema, as they consider the d-cinema investment to be large enough as it is. Therefore peripheral units specially dedicated to audio connections have been designed, to facilitate the additional features of digital cinema. Their function is to offer additional connectivity and sound processing features for professional and consumer equipment, without having to buy a new processor.

Connecting external audio to a Dolby CP650 or older processor

As we have seen before, apart from the most recent digital installation, most cinemas are equipped with a sound processor that was not specifically designed to manage audio signals for alternative content. This is for instance the case for the Dolby CP650 and models that preceded it.

To connect audio from a DVD player or game console, for it to be processed by the cinemas sound processor, amplifiers and speakers, the projectionist needs an additional peripheral device. Several products of different brands exist. One of the best known and most used ones is the Dolby DMA8Plus Digital Media Adapter.

Besides being able to handle the sound of the digital cinema server, that can be looped through, the DMA8Plus can manage sound from all kinds of players, process it if required and then forward it to the regular cinema sound processor. It is connected via a 25-pin cable to the "6 channel audio input" of the audio processor.

Features of the DMA8Plus include:

• Digital to analogue conversion for up to eight channels (sound of the server sent to the processor)
• Dolby Prologic, Dolby AC3 and Dolby-E decoding
• SP/DIF, Optical AES3 and Discrete inputs
• Output level matches cinema processor
• Individual delay setting for each input
• Correction of errors using setup software

Among the most common problems that the DMA8Plus can correct, is adjusting the global audio delay (varying from zero to 250 milliseconds maximum). This is usually caused by a difference in processing time between video and audio. So if the projectionist encounters a synchronization image / sound issue during a live broadcast, he can set the delay using the DMA8Plus set up software:

Dolby DMA8Plus menu with adjustable delay (top right).

Left: coaxial cable with RCA plug.Right: optical cable. 

The DMA8Plus has three main inputs:

• S/PDIF Optical or TOSLINK (input 4): To connect audio from a dvd or Blu-ray player, a satellite receiver, game console ...
• 2x AES (input 2 and 3). This version of AES called AES-3id uses a coaxial cable to a BNC connector and is used in broadcasting to make secure connections. This input is suitable for professional video players (HDCAM etc...) because it has a good protecting against the risk of noise. In addition, even if the cable that is used to connect a device to the DMA8Plus is long, the risk of degradation of the audio is very low.

For audio connections from peripheral equipment like DVD player and satellite receiver, the projectionist might have the choice between S/PDIF optical and coaxial, although the latter is less common. So what is the best option?

An optical connector is technically superior because it uses light to transport the sound. Therefore, there is no risk of electromagnetic interference.

The AES coaxial inputs are dedicated to professional players because of a superior noise immunity and a robust signal even with long cables.

Rear panel of a DMA8Plus : a Sony Playstation 3 is connected to the DMA8Plus with an optical cable (white circle).

As each player has his own input, the projectionist can easily switch between sources by pressing the right button (di >>>

Even though the Dolby DMA8Plus can be found in many projection booths, it is not the only media adapter available. USLs ECI-60 is about half the price of the DMA8Plus and can therefore be the right choice for budget wise cinemas. It is however less intuitive and configurable, and it cannot decode broadcast format Dolby E. But this is a format that you will not come across in cinemas very often, apart from the occasional film festival that also screens tv shows.

Cheap options to hook up audio

Some view professional media adapters as having some unnecessary features, and consider them only necessary to be able to connect audio signals which regular cinema processors cannot handle. Although there must be more home cinema and computer brands used in cinema, the German brand Teufel has a great and cheap product that has found its way into many (smaller) cinemas. For less than 200 euros the Decoderstation 5 can handle all your alternative content sound formats; it has inputs for TOSLINK, coaxial and stereo and can even process DTS - something the Dolby DMA8Plus for obvious reasons cannot and will not do.

Teufel Decoderstation 5; a cheap converter option.

Homemade 6 x analogue to 25 DIN cable.

Although not meant for cinema, a disused AV receiver can perform simple conversion tasks as well as some more professio >>>

The Decoderstation 5 is really nothing more than a computer audio card in a case, that converts consumer audio to 6 analogue signals, a format that can be plugged into the Dolby processor via a home made cable. Naturally, consumer products might be less reliable than professional products, that generally use better components. However, some consumer products can be useful in cinema environments.

A real low budget option, for instance for small arthouses that are short of cash, might also be to use a (disused) home cinema receiver to convert TOSLINK to 6x analogue audio.

Finally, there are some fine simple audio products that might come in useful. A converter from coaxial to optical might come in handy when you only have an S/PDIF input available.

Although not meant for cinema, a disused AV receiver can perform simple conversion tasks as well as some more professio >>>

Left: a cheap converter from Coaxial to optical.Right: Great optical switch to connect multiple Toslink digital s >>>

When only one optical input is available, this simple switch can be useful. All equipment can stay connected, while a simple twist of the central button selects which input is used.

Connecting audio to modern processors

The Dolby CP750, Datasat AP20 and QSC DCP 300 are all modern audio processors that were designed to handle digital cinema sound plus sound for alternative content, without the necessity for a media adapter. They can handle the audio from the digital cinema server (up to 16 PCM channels) and connect and process external sound (generally in Dolby Digital, Pro Logic III, Dolby Digital Surround EX, some even DTS HD). Please note that these processors can no longer process 35mm sound formats, but can connect to conventional cinema processors that perform that task.

Advantages of this type of installation are manifold : there are fewer cables and settings are easier because all the elements and settings related to sound (most of the time except 35 mm) are in a single processor. Thanks to its ethernet input modern processors like the Dolby CP750 can be connected to a Theatre Management System, which opens up many possibilities, like adjusting the volume remotely.

On the rear panel of the Dolby CP750 similar inputs as on the DMA8Plus can be found:

• An S/PDIF optical input.
• Two AES inputs (coaxial), for professional video players.
• An analogue stereo input called "NONSYNC" (for connecting background music).
• An XLR input to connect a microphone.

Dolby CP750 processor; above a USL dedicated alternative content processor.

QSC rear panel with top left: XLR microphone input, stereo analog input and a S/PDIF coaxial input (no optical).

This possibility to connect important consumer audio formats and thus alternative content is found over the entire range of modern audio processors. Many models exist, some are better known than others. The current offer is diversified enough so each cinema can make the appropriate choice according to their needs and means.

The two audio articles in the In Practice / Peripherals section were written in colaboration with Frédérick Lanoy of www.manice.org. Proof reading and advice: Jos Peters (ssjp).

One of the most popular devices to hook up to a digital cinema projector is the laptop or desktop computer. This is because by projecting images from a computer, an exhibitor can utilise his auditorium for rental situations in the so called 'dark hours', for hardly any cost at all, as he no longer has to rent a beamer. And the image quality is often far better than that coming from a beamer.

However, this can lead to a lot of hassle in the cinema. The main issue is that - naturally - cinema staff want the image on screen to look as good a possible. In order to get a good quality video signal, they generally want the computer to be placed as close to the projector as possible: in the projection booth. Sometimes one can allow for a preview monitor for the presenter, via a signal splitter in the projection booth.

However, the person doing the presentation will want to see and be able to control his presentation directly on a laptop in front of him - most often even his own laptop - which means that the laptop needs to be in the auditorium. This seems incompatible, and it is definitely not plug and play. In this chapter we will discuss the different ways to connect a computer, both in the projection booth and in the auditorium itself, and even discuss a solution that seems to have 'the best of both worlds'.

Cabled connections generally involve laying a cable from the front of the auditorium to the projection booth, which is not always easy - no door between the projection booth and the auditorium, the obligation to drill a hole in the wall, which might not be allowed by the fire department. Cables on the floor may also pose a safety problem to the audience. The ideal solution would be a permanent installation, where the video cables run in ducts, hidden in the walls of the auditorium. They would run from the projection booth up the screen. However, this is an expensive solution, so exhibitors generally look for simpler means.

A laptop image is visible on the cinema screen

Various inputs of the computer: LAN, VGA and HDMI

Traditionally in cinemas there is no direct connection between the projection booth and the auditorium, unlike for instance in theatres. This situation has its roots in the fact that 35mm film was a flammable substance and film projectors can be noisy machines, that by the sheer noise that they make can disrupt a screening. However, some cinemas are lucky enough to have a door in the projection booth that takes you directly to the auditorium. For all the others: when laying cables, you obviously need to make a permanent or semi-permanent connection between the projection booth and the auditorium. Make sure that your fire department is okay with the hole in the wall that you make, or you will get an unpleasant surprise when your site gets a routine check and might be marked as a fire hazard.

When laying a cable between the projection booth and the screen, more often than not the distance covered is very long and therefore the cable needs to be long and therefore of good quality. This cable can either be permanent, or temporary and needs to be durable. Beforehand, one should check what the maximum cable length is for the video signal that one wants to transport. When laying cables, and one has to make a hole in the wall anyway, it is useful to immediately lay multiple cables, like a power cable, mini-jack audio, XLR audio, internet etc, so you only have to lay cables once. Generally the hole has to be closed again afterwards with fire resistant materials and you won't easily get a second chance like that.

Available outputs on computers: Which are used to connect a digital projector or scaler?

A laptop offers a number of video outputs. The most common ones are VGA (also called D-sub) and DVI, which is increasingly being replaced by HDMI.

The projectionist must have a wide array of materials at his disposal to ensure that he will be able to handle all different connections. Indeed, if a client comes with a computer equipped with an HDMI output and the projectionist does not have a HDMI / DVI adapter to connect to the scaler or projector, he will therefore not be able to make the connection between the different devices. Anticipation of technical needs is therefore paramount.

To reduce the risk of accidental disconnection during the event, screw connectors are preferred. Unfortunately, the now ubiquitous HDMI connector has no screws to secure the connector to the computer.

HDMI

When considering a cable connection HDMI seems to be the best option, because it can handle HD signals with a very low risk of quality loss. However, HDMI was designed to connect a source (for instance a Blu-ray player) to an HD flat screen or video projector at close range. That's why most HDMI cable are quite short (less than 3 meters). Using this solution for presentations with a digital cinema projector means that the projectionist needs a very long cable (often more than 20 meters). These cables are quite expensive, especially if the cable is of good quality (gold plated connectors, good materials used for the actual cable). In addition, some computers don't have an HDMI output, although it's becoming more and more common. In case the computer has no HDMI output, the projectionist could use an active VGA - HDMI converter. However, these are not common in cinemas.

To sum up:

• Excellent results
• However, it needs a high quality cable, which are expensive at those lengths
• Fairly expensive solution

HDMI connectors have grown out to be a common computer interface

VGA connectors are great for showing PowerPoint presentations

VGA

VGA has long been the favoured means to connect a laptop to a d-cinema projector. This was the case because it was the most common connector on laptops and because it could easily be connected to video scalers. As Series 2 projectors can handle digital video signals through their external inputs, video scalers are becoming less common now in cinemas and less people are using VGA.

VGA is traditionally the most common way to connect a desktop computer to a monitor. Therefore, VGA-cables are traditionally very short (less than two meters) and the cable is often a low cost cable (for instance no gold-plated connectors). For a digital cinema presentation, the cable generally needs to be very long, as the projector in the booth has to be connected to the laptop in the auditorium.

Even if the projectionist uses a high quality VGA cable, the resulting image on the big screen will show some interference. As VGA is an analogue connection, the risk of a considerable loss of quality when using a long cable must be taken into account. In addition, VGA cable can't handle digital HD signals, which can become a problem with modern computers which only have digital connectors. And: the maximum cable length gets shorter as the required resolution becomes higher.

To sum up:

• Fair results with high quality cable and when the distance between projection booth and the costumer's computer is not too long (small auditoriums)
• Avoid this connection with demanding costumers and HD content

A laptop connected to an external source via VGA

VGA amplifiers help to carry VGA signals over long distances

VGA with amplifier

With VGA still being a common external video connector on laptops, it's a shame not being able to use it in large auditoriums. This is particularly true as PowerPoint presentations account for maybe 90% of the content that people want to show on screen and therefore a video signal from a VGA connection is good enough. A long, high quality VGA cable plus a VGA amplifier should do the job. The VGA amplifier is installed near or behind the screen - a little concealed - and the laptop is connected to it using a standard VGA cable. The long VGA cable then connects the VGA amplifier to the video scaler.

To sum up:

• Good enough image for SD video
• Good alternative as a permanent option in your main 'presentation' auditorium
• Not future proof, as images will be more and more digital

LAN (RJ 45) cable

In digital cinema, ethernet cable is mainly used as a communication connection between projector and server and to create a network between all the screens of a cinema. The projectionist can transfer DCP's from server to server or from the central library to the servers. The main advantage is the massive data rate that the RJ 45 (or LAN) cable allows (up to 1000 Mbits per second). In addition, it's fairly strong and secure (safelock), reliable and quite cheap (compared to for instance HDMI).

Video and audio can nowadays run reasonably well over network cables. For this, two VGA / RJ 45 Extender units are used. A long ethernet cable connects the two (the first in the auditorium with the computer, the second in the booth near the scaler). Two standard VGA cables complete the link between the extenders and the equipment.

The advantage of this method is that it replaces the VGA cable in the 'VGA amplifier' system by the RJ 45 cable, which is much less sensitive to signal degradation over long distance. Therefore its use seems perfectly appropriate in this type of configuration.

However, use of HD content is limited. In addition, as the length of ethernet cable increases, the resolution will tend to decrease. Also note that nowadays there are also extenders for HDMI and DVI, which we will not discuss here, but which might grow out to be a great option for the future: HDMI - HDMI connections without converting.

VGA extenders use LAN cable to carry VGA signals over long distances

RGBHV can be used for VGA as well as for HD video signals

RGBHV cable

One side of the high quality RGBHV cable connects to the scaler, the other to a unit that extends VGA via the RGBHV cable. Kramer and Extron have these converters with and without horizontal shift, as the image can move horizontally when using different resolutions, which you can then correct with the shift button.

Apple

Even though in rental situations one should always ask customers wanting to use their own equipment to bring it in a day early, this is particularly the case with Apple computers, as these generally have different connectors than Windows computers.

Some presenters like to use their own computers, like this guy with his Mac

Mini-VGA can be found on early Apple, Sony and HP laptops

Available outputs

Mini-VGA

can be found on early Apple, Sony and HP laptops. It can also be used for NTSC-PAL video output (S-video Y/C or composite CVBS).

Mini-DVI

supports resolutions up to 1920x1200 @60 Hz and can be converted to VGA, DVI-D and video.

Micro-DVI

is the rarest of the bunch, and was only used for a short period of time on the first Apple Macbook Air (Jan/Oct 2008) as well as on some Asus laptops. It can be converted to DVI-D with an adapter

Mini-DVI supports resolutions up to 1920x1200 @60 Hz

Micro-DVI to DVI-D adapter

Mini DisplayPort (or mDP) is a custom socket & connector, also licensed to Toshiba, HP and Dell

Mini DisplayPort

(also called mDP) is a custom socket connector by Apple to replace the DVI ones, but is now also licensed to Toshiba, HP and Dell for use in their laptops. It drives resolutions up to 2560×1600 (WQXGA). Adapters are available to Dual-Link DVI-D, DVI-D and to VGA. Since it also supports audio out (since April 2010), Mini DisplayPort is compatible with HDMI, and adapters are available. Please note that Mini DisplayPort's HDCP extension disables playback of certain DRM-encrypted content on any display or projector that doesn't support HDCP. Mini DisplayPort adapters do not exist for SD video output (component video, S-Video, or composite video) connectors.

Apple laptops will by default use the monitor output for a second screen to the desktop. To clone (mirror in Apple lingo) the laptop´s desktop or adjust the output resolution and frequency of both screens, point your mouse to the Apple icon in the top left corner in the menu bar, press the (left) mouse key and release over "System Preferences". There you select "Displays".

Sound output: mini jack

For customers who want to screen content with sound, the projectionist needs to connect the cinema's audio processor to the computer. The most obvious solution is to use the headphone output of the PC. It is present on all computers. To make the connection with the processor, the projectionist must run an audio cable to the projection booth. To make this job easier, it makes sense to run it along with the video cable (VGA, HDMI or RJ 45). It will be easier for the projectionist to run multiple cables.

Since there's no mini jack connector on cinema audio processors, using a Mini Jack / XLR cable is the best option.

Mini jack outputs can easily be used for simple sound signals

A mini jack to XLR cable plugs directly into the mixer

A mixer can be connected to the cinema audio system via XLR

The main advantage of using a mixer is that other audio sources like a CD player (for background music) or microphones can also be connected. XLR connectors provide the connection with the processor, and each input can be individually adjusted. Thus, the projectionist has the possibility of lowering the noise level of background music, or allow the customer to use the microphone to publicly discuss video images. It becomes easier to meet the customers requirements.

If it's not possible to connect the computers audio directly to the mixer, for instance because the mixer is in the booth and the PC in the auditorium, there is a second option. This is to use the audio pack of a wireless microphone, which generally also uses mini jack, but needs a special cable to send the signal to the booth. As this is professional equipment, the risks of interferences are low. The receiver of the wireless microphone can then be put in the booth and used to connect to the mixer.

To display an image from a laptop, firstly the external video output has to be activated. On most laptops this is done by pressing Ctrl F5, though one should be aware of Linux or Apple laptops that a client might bring in and are operated differently. Now the computer has made a secondary video signal available to be displayed. A computer can generally offer the external video signal in two different ways: as an 'extended desktop', or as a clone of the desktop. The second option is often favoured, as it makes the same image that is shown on the computer available to be displayed.

Once an external video signal becomes available, the resolution of the image and the refresh rate (frequency) can be changed. Naturally, the maximum resolution and refresh rate depends upon the quality of the computer. One should however realize that more is not always better. For a PowerPoint presentation, using a 4x3 screen a resolution of 1024 x 768 is often sufficient, while for a 16x9 screen a resolution of 1280 x 720 can be enough. One should also realize that the people in the audience should all be able to read the text that is projected on the screen, which might not be easy at 1920 x 1080 resolution.

The scaler (bottom left) handles the signal from the computer and sends it to the projector

The video scaler

Indeed, different devices don't necessarily recognize each other automatically. Among the sources of potential problems are often:

Misconfiguration of the video output of the computer

A computer is not primarily designed to stream content onto a digital projector. When connecting the device to the scaler or directly to the projector, it is possible that the source (the PC) is not recognized by the device (the projector). Thus, to force detection, the projectionist can manually activate the video output of the computer by pressing Ctrl F5.

This procedure applies to most equipment, but not necessarily to computers running Linux or Mac... Again, it's important to have the equipment at the location beforehand to test it and avoid unpleasant last minute surprises.

If Ctrl + F5 doesn't work, one has to enter menus on the computer to manually force the activation of the video output. The procedures vary widely among operating systems and versions of these systems (XP, Vista, Windows 7 ...).

For example, on Windows Vista, go to Control Panel / Appearance and Personalization / Customization. The "Connect to a projector or other external display device" appears in the upper left. One should then activate the display parameters.

A computer can generally offer the external video signal in 2 ways: as an 'extended desktop', or as a clone of the desktop. The second option is often favoured, as it makes the same image that is shown on the laptop available to be displayed.

Although there is a wide variety computers on the market, this is nevertheless a universal procedure, that can significantly increase the chances of recognition between the PC and the scaler or projector. Wherever possible, the computer must be turned off when connecting. When it is turned on, it should normally automatically detect the device which it is attached. This is made possible through a protocol called EDID, which facilitates the exchange of information between computer and screen.

EDID data exchange is a standardized means for a display to communicate its capabilities to a source device. The premise of this communications is for the display to relay its operational characteristics, such as its native resolution, to the attached source, and then allow the source to generate the necessary video characteristics to match the needs of the display. This maximizes the functional compatibility between devices without requiring a user to configure them manually, thus reducing the potential for incorrect settings and adjustments that could compromise the quality of the displayed images and overall reliability of the system.

Poor resolution or poor refresh rate of images that create a 'black screen'

There are a wide variety of computer resolutions ranging from VGA (640 x 480) to HD (1920 X 1080) on more modern models. In addition to resolution, setting the refresh rate of images is another decisive factor in the quality of the images on the screen.

When connecting the computer to the scaler, auto detection should normally identify the technical characteristics of the signal source. The role of the scaler is to process the signal and to send it to the projector in the best possible configuration (resolution, colour ...).

The "In Auto Acquire" function of the ACS-2048 scaler can automatically detect all the sources connected to its interfa >>>

VGA without security screws

Faulty connections

Connecting a computer to the digital projector involves the use of cables. In the context of seminars and presentations, they are often displaced: cables are layed in the auditorium, reassembled, wound up... Over time, all this handling can end up damaging them. This concerns not only the connectors (plugs damaged) but also the protective sleeve which degrades (spectators walking on cables, cables pulled abruptly and torn...).

When computer and scaler (or projector) don't make a connection, the cable can simply be defective. In an attempt to identify the source of the problem, it makes sense that the projectionist has several cables of the same length and nature (VGA, HDMI, DVI, RJ 45). By exchanging the cables, the source of the failure can be found.

To avoid unpleasant surprises (a projectionist lays a VGA cable of 40 meters up to the screen, to realize that it no longer works), it is advisable to do a quick test with the devices plugged in, in the projection booth. This saves valuable time and avoids the operator to lay a new spare cable.

Another well known source of black screens is bad connections of the connector. To save space on the side panel of laptops, manufacturers are more and more eliminating screwed connections for VGA connectors.

In the case of a loose connector, the slightest movement of the computer can cause to lose the video signal and thus the image on the screen. This therefore causes problematic situations in full view to the audience.

Non-secure connection: the slightest touch will cause a black screen

Be careful not to reverse the transmitter and receiver boxes!

Improper connection of the amplifier

Some solutions require the use of signal amplifiers. Their role is to amplify the video signal while passing through a cable, so that it remains at a satisfactory quality level despite the distance between the devices.

The boxes are generally not self powered. They are electrically connected to the mains through transformer (5, 9 or 12 volts). A faulty connection or using the wrong transformer can prevent the transmission of the signal and cause a blackout.

The use of these boxes also means that one has to respect the polarity. There is a transmitter and a receiver box. If the projectionist gets this wrong, the video signal will not be transported.

If despite all efforts, the operator fails to establish a connection between different devices, there is always the possibility of transferring the clients files onto a usb stick, for playback on another computer. This has many benefits for cinemas; it seems essential that the projectionist has a laptop as a solution to fall back on.

Finally, here are some tips for what one should keep in mind when using laptops for rental situations.

• Main advice: installations should be done by a professional
• Make sure that you know the password of the laptop that you use
• Not all resolutions and frequencies are supported by video scalers. 'Just stick a laptop in it' can have nasty consequences
• Test everything out in advance.Therefore ask for the equipment in advance!
• Does the person who will do the presentation just want a picture, or also sound? Ask in advance and not on the day itself
• Turn off the screen saver of the laptop. Adjust the power properties of the laptop to 'Always on'
• Make sure as few as possible applications are running in the background on the laptop
• Always use an AC adapter; don't rely on the battery of the laptop. However: when there is a hum in the audio, a 'ground loop' through the power cord might be one of the possible causes
• Use professional cables and adapters and mark these with the name of the cinema
• Turn off the system sounds of the laptop
• If they want to show (internet) video, let them use their own laptop because of the many video codecs that are on the market
• Use one single laptop per event, do not change laptops at every presentation
• Don't forget to light the speaker :-)

Wireless networks are everywhere nowadays: Wi-Fi, 3G on cellular phones, and on laptop computers... Wireless signals can transport images and sound with high quality; some can even transport high definition image (1080P). For digital cinema presentations, using a wireless solution is an appealing idea. It seems to be easy and practical for the cinema and the projectionist. Unfortunately, at this time a wireless solution is not reliable enough, for many reasons.

The main reason is that a cinema auditorium and a projection booth are places with a lot of electrical equipment: speakers, projectors (35 mm, digital), sound processors, amplifiers... The environment (curtains, carpet...) can also create interferences.

More annoyingly: when testing before the event, the projectionist does so in an empty auditorium. If everything is OK, this normally guarantees that the show will proceed with no problem... except when using a wireless system. During the event the auditorium will be full of people and therefore full of cellular phones, which can create interference in the presentation. In the future wireless audiovisual systems might be the way to go, but for now it's better to stay away from them.

Remote control

Although it's best to stay away from wireless video connections, remote controls can be very useful in cinemas. As was mentioned before, the best video signal quality is obtained when the laptop is placed close to the projector or scaler. Therefore, a common option is to use a remote control. This is a great cheap and easy way to connect a laptop, and a popular choice with cinemas that are just starting with digital cinema. The additional advantage is that no cables need to be pulled.

When using a remote control, the laptop is placed in the projection booth and the presenter is given a remote control with which he can control his PowerPoint presentation. For presentations this is generally no problem, as all the presenter wants to be able to do is click to the next slide. If the presenter needs to point out something on the screen, some remote controls are equipped with a laser pointer.

Traditionally remote controls (sometimes even called 'presenters') cater for the office market. Therefore manufacturers have long focused on devices for short distances, that would only work in small cinema auditoriums. These presenters were pretty straight forward in use, generally featuring a usb stick that needed to be connected to a usb port and you were ready to go - the laptop saw it as a computer mouse.

On the other end of the spectrum were sophisticated and expensive presentation kits, that more or less replaced the laptop itself. These kits can cover the whole distance of large auditoriums, but as said they come at a price. Also: these kits generally need software to be installed on the computer, which is not always useful in a rental situation, if someone turns up with a Linux or Apple laptop...

With technology moving on, recently new cheaper 'presenters' have come on the market that will cover the entire distance of large auditoriums. This new Logitech presenter covers 30 meters and therefore will work in front of the screen of most auditoriums. Additional advantage: it is generally available from your local high street electronics store.

New presenters cover the distance of entire auditoriums (30 meters)

The presenter consists of a handset and a usb stick (sender and receiver)

The receiver simply plugs into a usb port and then acts as a mouse

As good as modern presenters are - and every digital cinema should have at least one - they still leave the person in front of the screen feeling that he has to deal with a surrogate of his own computer. Therefore most cinemas will, at some stage turn to more sophisticated connections, whereby the laptop can stay in the auditorium. An alternative can be to allow the presenter to use a remote control unit, but have a review monitor on stage, so he can face the audience and doesn't have to turn to face the screen every time a new slide comes up.

Apps

Remote control app

Over the last couple of years, especially since the introduction of the Apple App store in the fall of 2009, apps on mobile phones have gained huge popularity. Some apps, also available on platforms like Blackberry and Android, have been especially designed to control electronic equipment like laptops or the software that runs on it. In this chapter we 'll discuss the use of Apps. Please note however that, as has been said in earlier chapters, wireless networks - as used by apps - are not as reliable as wired ones.

We pointed out earlier that there's a discrepancy between the fact that people giving a presentation generally want to be able to see and control it themselves, while in order to get a good video signal we generally prefer the computer with the presentation to be as close to the projector as possible, i.e. in the booth. Using apps, a presenter gets to see and control his his presentation much more then when using traditional remote controls or so called 'presenters'. As it's impossible to discuss all available apps, we'll focus on some Apple ones as an example. Android or Blackberry apps might have similar functionality, though naturally differences remain.

Apple's Remote app turns an iPhone, iPod touch or an iPad into a remote control for iTunes or Apple TV. You can select songs, playlists, play video or broadcasts, choose different speaker sets and control the volume. In fact everything that is playable through iTunes is accessible via this app. Download the app from the Apple appStore (it's free) and you're in business. It is possible to use multiple iPhones or iPads simultaneously.

Remote App interface on iPhone. Music interface with progress bar, repeat function, shuffle function, cover art, volume >>>

Remote App interface on an iPhone. iTunes playlists. The iPad shows a similar interface, only much bigger and with an o >>>

Keynote Remote app displaying current slide and presenters' notes.

Keynote Remote app

When giving a presentation, you can use the Keynote app to control your slides with an iPhone, iPad or iPod touch. Functions are Forward, Rewind, Start and Stop. You can also view your notes connected to the particular slide currently displayed. This makes paper notes superfluous.

However, there is a catch: you have to run the Apple programme Keynote for your presentation. Fortunately Keynote is capable of handling Microsoft PowerPoint presentations, although complex transitions might not be supported, in which case Keynote will simply ignore them and move on to the next slide. The Apple Keynote Remote app is free. You can use it with more than one iPhone or iPad at the same time.

A final option to control a laptop is one that combines advantages of all connection options that we discussed before, and that was touched upon in the section about apps. Using remote access on a computer, a presenter in the auditorium can access and control his presentation directly. But as that computer is used to control a second computer in the projection booth, the video signal can be exceptionally good. The only drawback is that you need two computers for this to work.

When setting up a remote access connection within a building, for instance for our purpose of connecting a computer to a D-cinema projector, it is tempting to use the internet to make the connection. Many auditoriums nowadays have internet connection and most people are familiar with setting up an internet connection on a computer, which sometimes is as simple as connecting a LAN-cable. However, using the internet for this purpose can result in lagging of the signal (the on screen picture changing seconds after the presenter has pressed for the 'next slide') and in extreme cases even in a lost connection, when the internet is down.

It is therefore better and even safer to set up a direct connection between the computers, preferably using a cable and not Wi-Fi. Next to better reliability, a cable connection allows for more bandwidth, which means a better image with smooth transitions.

The settings of an Apple computer are set to allow VNC connections protected with a password

The desktop of a guest Mac displayed on a Mac running Apple Remote Desktop software

Remote Desktop

In computing, the term Remote Desktop refers to a software feature allowing graphical applications to be run remotely on a computer, while being displayed locally. It is found on almost all computers regardless of make or operating system and works using network technology like Wi-Fi, Ethernet or TCP-IP.

The features of Remote Desktop applications may vary. Some allow attaching to an existing user's session (i.e. a running desktop) and "remote controlling" it in front of the user's eyes. Although Remote Desktop was originally intended to be used for support functions, enabling expert users to fix computer problems remotely, it can be helpful for presentations too.

Using Remote Desktop you can not only monitor and control your computer in the projection booth running your presentation, but any other computer anywhere in the world. The computer might be located in the auditorium, but might just as well be the computer that you use for selling tickets at the box office or the one playing background music at the cinema bar. Remote Desktop is easiest to operate if the two computers are located in the same network, so you don't have to deal with firewalls, which can potentially block external access.

This is how it works: the controlling computer generally displays a copy of the image received from the controlled computer's display. This copy is updated on a timed interval, or when a change of screen is noticed by the remote control software. The software on the controlling computer transmits its own keyboard and mouse activity to the controlled computer, where the remote control software implements these actions. The controlled computer then behaves as if the actions were performed directly on that computer. Depending on how it is implemented, displays connected to the controlled computer can show what the controller is doing, or be disabled in order to hide actions and lock out users in front of the terminal.

Although Remote Desktop is extremely powerful and can be used for our purpose, it does require some expert knowledge about computers and networks. Therefore it should only be used if everyone in the projection booth can operate it.

Setting up Remote Desktop in Windows

As Remote Desktop comes with every Windows computer and more user friendly software with similar options comes at considerable cost, we'll discuss how Remote Desktop functions.

You need two things to create a remote location:

1. Microsoft Windows XP Professional, Vista Ultimate or Windows 7 must be installed on the computer. The computer must also be part of a corporate network in which Remote Desktop connections are permitted. This computer is known as the host.

2. The remote (auditorium) computer must be running Windows 95 or later. This computer must also have the Remote Desktop Connection client software installed. The remote computer is known as the client.

To set up Remote Desktop start with the host computer, which in this example is your projection booth computer.

• Verify that you are signed in as the administrator
• Click 'Start', then 'Control Panel'
• In the Control Panel click 'Performance and Maintenance' and then click 'System'
• Click the 'Remote' tab, then check the 'Allow users to connect remotely to this computer' check box, and then click OK

Next, you have to make sure that you have set up the Windows Firewall to allow for exceptions.

• In the 'Control Panel', click 'Security Center'
• Under 'Manage security settings for', click 'Windows Firewall'
• Make sure that the 'Don't allow exceptions' check box is not selected
• Click the 'Exceptions' tab, and verify that the 'Remote Desktop' check box is selected
• Click OK, and then close the Windows Security Center window. Your host computer is now set up to allow remote access

You will now need to find the name of the host computer.

• In the 'Control Panel', click 'Performance and Maintenance'
• Click 'System', and then click the 'Computer Name' tab
• Write down the full computer name, and then click OK
• Close the Control Panel' and leave this computer running, locked, and connected to the corporate network with Internet access

To connect your auditorium computer, which is the client (or remote) computer to your projection booth (or host) computer, follow these simple steps:

• On your auditorium computer, you need to find the 'Remote Desktop Connection' in the 'Accessories' menu (Start / Programs / Accessories)
• In the 'Computer' box, type the computer name or IP address of your host computer and click 'Connect'
• When the 'Log On to Windows' dialog box appears, type the user name and password of the host computer
• The 'Remote Desktop' window now opens, and you see the desktop of your host computer, which in this example is your projection booth computer

If Windows Remote Desktop seems hard, you probably you need to know something about networking first. It is also useful to print the IP address, name of the network, log-in and user name of the projection booth (host) pc, so it's available for every projectionist when required.

IP addresses and DHCP

Until now we were assuming that you were using cinema equipment, that is generally connected to the cinemas own network. So what if someone brings in their own computer for a presentation?

Most computers network settings are set to receive an assigned ip address, a computers unique identifier. These ip addresses are generally given out by the router or modem that connects you to the internet. The part of the router that assigns these addresses is called the DHCP (Dynamic Host Configuration Protocol) server.

Therefore, if someone brings in their own computer to your cinema, more often than not it's waiting to have an ip address assigned. In order to use the computer for remote access without using the internet - as that slows connections down - we need it to have an ip address, as otherwise the other computer cannot find it. These ip addresses need to be in the same range, for instance 192.168.10.12 and 192.168.10.15.

There are two ways to go about giving the computer an ip address. Maybe the easiest way is to manually give the computer an ip address. For this, we first look at the ip address of the computer that the guest computer needs to be connected to. This can be found in the properties of the network adapter. We then open the network settings of the guest computer and give it a static ip address, in the same range as the cinema computer. The computers can then be directly connected to each other using a LAN cable.

If one doesn't want to change the network settings, one can easily connect both computers to a router. The router's DHCP server will then automatically assign ip addresses to both computers, facilitating identification.

It's important to understand the difference between a router and another network device: a switch. When an internet signal is distributed within a building to multiple computers, one generally uses a switch. This is a piece of equipment of a much simpler design than a router. A switch can be compared to cross roads, directing parts of the signal in certain directions and other parts to other directions. A switch lacks a DHCP server and can therefore not be used for remote access.

Commercial remote access software

When setting up a remote desktop connection is too diffucult for you or if you find its options too limited, you can choose to use commercial remote access software. We will discuss the best and most used ones.

TeamViewer

One of the best and most user friendly remote access software suites on the market is TeamViewer. It can be used to perform remote access tasks without the user needing to have any real computer knowledge. Before briefly explaining how it works, it should be noted that TeamViewer is free for private use only; commercial licenses start at 500 euros.

When using TeamViewer, one should install the software on both computers that one is going to use. The software on the host computer automatically shows the ip address of the computer on its opening screen and generates a one time only password, that needs to be entered in the remote pc's software. TeamViewer can then find the host pc anywhere in the world, even when it's located behind a firewall. There is no need for the user to know anything about network protocols or ip addresses. TeamViewer makes a one time only connection, so after disconnection a new password is required to reconnect.

TeamViewer is platform independent; there are versions for Linux and Apple. Lately a great number of different versions of TeamViewer have come on the market, each with its specific functionality. There is for instance a Host version for stand alone computers, a QuickJoin version for on-line presentations and a portable version for mobile use. TeamViewer Quicksupport doesn't even require installation and as it can be run from a usb stick, it's ideal for rental situations.

The TeamViewer panel showing user ID and password

Ultra VNC is very configurable, but maybe also a little overwhelming

VNC

VNC (Virtual Network Computing) is also platform-independent remote access software. it was originally developed by the Olivetti Research Laboratory (UK), but its original source code and many modern derivatives are open source and distributed under the GNU General Public License. There are a number of different companies that have further developed the software. Some of the best known ones are Ultra VNC (free), Tight VNC (free) and Real VNC (not free; commercial licenses start at €38,-).

A VNC system consists of a client and a server. The VNC server is the program on the computer that shares its screen. The server passively allows the client to take control of it. The VNC client (or viewer) is the program that watches, controls, and interacts with the server.

There are clients and servers for many operating systems and also for Java. A VNC client on one operating system may connect to a VNC server on the same or any other operating system. Multiple clients may connect to a VNC server at the same time. These days its even possible to use an iPhone or iPad to access your computer at home.

There are a number of variations of VNC from different software companies which offer their own particular functionality. Most are compatible with VNC in the sense that a viewer of one flavour can connect to a server of another type. So when you have a VNC server installed on your projection booth PC, it can be controlled in multiple ways, using an auditorium laptop or for instance an iPhone with VNC software from another vendor installed on it.

VNC programs are generally very configurable, but - therefore - not as easy to understand as Teamviewer. Before using them in a commercial setting, one should first get acquainted with it. As it's free, the best program for this is Ultra VNC. As its configuration options might be overwhelming, Tight VNC might be a good alternative.

The 4 articles in the Peripherals / computer-section have been created with the help of RdJ, BIJ, JB, TN and JP.