Tech Blog – TV/DVD Surround Encoding Technologies

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Paul Neyrinck provides an overview of the surround sound technologies often used in television and DVD

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.

DTS – This is used widely for DVD and BluRay.  Typically, 5.1 audio is encoded as a DTS data stream.  The DTS stream is encoded very efficiently so that it uses a small portion of the DVD bandwidth.  But it uses more bandwidth than AC3 and is often regarded to sound better than AC3.  But not every DVD player can decode DTS so DTS is often on a DVD as an alternate to AC3.  Every BluRay player can decode DTS.

DTS-HD / DTS-HD Master Audio – This is used for BluRay.  Typically 5.1 or 7.1 audio is encoded as a DTS-HD data stream.  The DTS-HD stream is encoded very efficiently so that it uses a small portion of the BluRay bandwidth.  A DTS-HD Master Audio stream is lossless and has no coding artifacts.  Every DTS-HD stream carries a legacy DTS stream so that it can play back on any BluRay player.

Dolby E – This is used for professional broadcast delivery on digital video tape, files, and satellite link.  It carries up to eight channels of audio and it carries AC3 metadata that can be used by a Dolby Digital encoding system for ATSC broadcast.