There have been many technologies developed over the years to deliver surround audio for television and DVD. The following is an overview of the technologies often used in television and DVD. You can find more information using Wikipedia. Surround encoding technologies are separated into two types: Matrix and Discrete.

Matrix Encoding / Decoding

Three or more channels of audio are processed and down mixed to a stereo signal which is often called a LtRt (Left total, Right total).  Any analog or digital stereo system can play the LtRt audio.  A decoding system can be optionally used to expand the stereo back out to three or more channels.  Matrix encoding technology was initially developed in the 1950’s and has been used mostly for delivering surround audio on stereo film soundtracks and with analog stereo television.  The matrix encode/decode process is not precise.  For example, audio that was originally only in the surround channel will have crosstalk into the decoded L and R channels.

Dolby Surround – Dolby Surround is a matrix encode/decode system introduced for television in 1982.  The encoder encoded four channels L, C, R, S to an LtRt for broadcast.  If the consumer watching TV uses a Dolby Surround decoder, it gets decoded to L, R, S.

Pro Logic – Dolby introduced Pro Logic matrix decoding for home theater systems in 1987.  Pro Logic decoding will expand an LtRt to L, C, R, S.

Pro Logic II -  Dolby introduced Pro Logic II matrix decoding for home theater systems in 2000.  Pro Logic II decoding will expand an LtRt to  L, C, R, Ls, Rs.

Pro Logic IIx -  Pro Logic IIx decoding will expand an LtRt to  6.1 or 7.1.  The extra channels provide better surround localization.

Pro Logic IIz -  Pro Logic IIz decoding will expand an LtRt to  9.1.  The extra channels are placed above the left and right channels for height localization.

DTS Neo6 – Neo6 matrix decoding will expand an LtRt to  5.1 and is similar to Pro Logic II.

Discrete Encoding /Decoding

With discrete encoding, one or more channels of audio are processed to calculate a data stream.  Typically, the encoding is “lossy” and can introduce small distortion artifacts, but lossless encoding is sometimes used with BluRay.  The data stream must be stored digitally as a file or as a stream on a digital video tape or DVD.  Because it is discrete, each channel is encoded separately and can be decoded for playback to the correct speaker.

Dolby Digital (AC3) – This is used widely for DVD and digital television (ATSC).  Typically, stereo or 5.1 audio is encoded as an AC3 data stream.  The AC3 stream is encoded very efficiently so that it uses a small portion of the DVD or digital TV bandwidth.  Every DVD player and ATSC  system can decode 5.1 Dolby Digital and downmix it for stereo playback.  Typically, the stereo down mix is an LtRt that is compatible with any of the matrix decode technologies.

The Neyrinck SoundCode For Dolby Digital and SoundCode For DTS plug-ins are fully compatible with Pro Tools LE.  This means you can offload surround DVD encodes to a smaller room while keeping your main Pro Tools HD room system for mixing.  This post goes over a few details to keep in mind when encoding and decoding with Pro Tools LE.

Any LE system can encode surround DVD’s because the encoding is performed as an Audiosuite plug-in.  Simply place the 6-channel mix in six mono tracks ordered from top-to-bottom L, C, R, Ls, Rs, Lfe.  Then select the SoundCode Dolby Digital or DTS plug-in from the Audiosuite menu and encode.

Decoding operates as an Audiosuite or RTAS plug-in so it works with Pro Tools LE.  But a standard Pro Tools LE system is stereo only and so the RTAS decoder will be limited to stereo.  But now that the Complete Production Toolkit (CPT) option is available, Pro Tools LE can support 5.1 tracks.  If you have the CPT, then you can easily use the 5.1 Dolby Digital and DTS decoder plug-ins.

Every Macbook/iMac/Mac-mini sold the past few years has an audio output that is specified as a “headphone/optical digital audio output (minijack).”  See here, for example.  Recently, I wanted to use this digital audio output to connect to my living room home theater receiver but found very little information about it.  I called two Apple stores in San Francisco and neither Genius knew about the feature and  could not explain how to use it or buy cables for it.  In this post I share what I learned after much online research and experimentation.

How It Works

From the outside, the minijack output looks and behaves like any tip-ring-sleeve analog audio minijack.  And the Sound Output panel in preferences does not indicate anything otherwise (my Macbook Pro names the output “Internal Speakers”.)  But deep inside the minijack is an optical output circuit that is not operational or visible until you insert a special plug.  You must insert a special plug that has a little hole on the end that goes deep inside and receives the optical light source.  Wikipedia calls it a mini-TOSLINK.  Amazon sells adapters and cables that call it optical mini.  If you insert this special plug, then the Mac detects it and magically changes the name of the output in the Sound preferences panel (my Macbook Pro changes the name from “Internal Speakers” to “Digital Out.”).

Getting The Cable/Adapter

Radio Shack does not sell them.  Best Buy does not sell them.  And interestingly, Apple does not sell them online or at the retail stores.  Apple used to sell a Belkin cable/adapter but apparently stopped as far as I could tell.  Thank goodness for Amazon who sells a few different cables and adapters.  But most amazing is the price.  For example, they sell a 6 Foot Toslink to Mini Toslink Cable for 51 cents.  I bought a 6-foot cable and a 12-foot cable for just a few dollars.

Using It For DVD Surround Sound

The Mac DVD Player application has a preference for audio output.  Normally, it just says “built-in output” on my Macbook Pro.  But if I connect the mini optical cable before launching DVD Player, the preference has an additional choice called “Digital Output.”  And when I connect to my home theater receiver, I can listen to 5.1 Dolby Digital or DTS soundtracks.  So now I am looking into a Mac-mini as a home theater playback system for files and DVD’s…more to come.

I hope this information can save someone time figuring out how to use this nifty feature available in millions of Macs.

SoundCode For Dolby Digital is a feature-rich tool for encoding and QC testing AC3 files for DVD.  One cool feature is that you can connect a DVD player to Pro Tools hardware and decode 5.1 surround directly in Pro Tools.  This is a great way to listen to your DVD before you commit to burning more copies or to listen to commercial DVD’s against your mix.  You can do this with an external DVD player or the DVD player in the computer as long as the DVD player has a SPDIF or Optical output.  The decoder plug-in is RTAS and will operate is stereo-to-5.1 mode in Pro Tools HD or Pro Tools LE with the Complete Production Toolkit.

Follow these steps to decode and monitor a DVD directly in Pro Tools:

1.  Connect the SPDIF/Optical output of the DVD Player to the SPDIF/Optical input of the Pro Tools interface.

2.  Launch Pro Tools and create a session at 48 kHz, 16 or 24-bit.  It is very important to use a 48 kHz sample rate.

3.  Open the Hardware Setup dialog and set for external sync using the SPDIF / Optical input that is connected to the DVD player.  It is very important to sync Pro Tools to the DVD player.  When you close the Hardware Setup dialog it should notify you that it has found the sync.  If it notifies you that there is no sync then you have not configured the sync correctly.

4.  Lower your monitor level and  create a stereo aux track in Pro Tools.  Set the input to come from the DVD player.

5.  Play a DVD and make sure you can hear an AC3 stream coming in from it which is full-code noise.  Be very careful to listen at a very low levelbecause the full-code noise can damage your equipment and hearing.  It is very important that you hear the AC3 stream.  If you hear normal audio then either the DVD player needs to be configured correctly to output the AC3 stream or the DVD does not have an AC3 soundtrack.

6.  Insert a RTAS stereo-to-5.1 SoundCode Dolby Digital decoder on the track.  Set the track output to a 5.1 interface path.  It is very important to set the output to a valid interface path.  Pro Tools will not run the plug-in if the track output is not connected.

7.  The STATUS section of the plug-in should indicate that the input is Dolby Digital and you should hear 5.1 audio.  If it says PCM, then the DVD player input has not been configured correctly.

Now you should be able to enjoy 5.1 sound from a DVD directly in Pro Tools.!