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What are the different mix formats I need to know about?
Your production will be viewed and heard on a wide variety of playback devices, from massive theatrical speakers and playback systems to tiny computer or video systems with one speaker and a paltry amplifier. While some productions will produce one mix to be heard under all conditions, major studios will commonly produce a variety of mixes for different formats, the most important distinction being between television viewing in the home and theatrical viewing.
THX is not a sound system or sound format. It is a standard for overall theater quality, which includes characteristics of screen brightness, projection characteristics, acoustic isolation, and other errata.
5.1 (AKA Dolby AC3) is the most important standard in use today, commonly used in DVD's, and as part of Dolby Digital and DTS theatrical systems. It consists of 6 discrete channels:
LEFT, CENTER, RIGHT, LEFT SURROUND, RIGHT SURROUND, and a SUBWOOFER.
5.1 is not compatible with stereo playback systems, but to maintain compatibility options, a stereo mix or LTRT (Left total Right total) always accompanies a 5.1 mix delivery element.
Dolby Stereo (also known as Pro Logic) has been the theatrical standard for motion pictures for over twenty years; today it is very commonly used in home playback systems as well. It consists of LEFT, CENTER, RIGHT, and a single SURROUND channel. By means of a patented matrixing encoder, this format is compressed and reduced down to 2 channels for distribution. When played back, a matrix decoder expands the 2 channels back out to 4 channels. This is sometimes referred to as 4-2-4.
One of the advantages of Dolby Stereo's 2 channel distribution format is it's compatibility with regular stereo and mono playback systems. Any film released in 5.1 must also carry with it a Stereo mix, so that the soundtrack may be played back on systems that are not 5.1 capable.
7.1 is known as SONY SDDS, another surround format consisting of LEFT, CENTER LEFT, CENTER, CENTER RIGHT, RIGHT, LEFT SURROUND, RIGHT SURROUND, AND SUBWOOFER channels, for theatrical distribution only. Command Post does not have 7.1 capability.