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The most common surround sound formats are described below.
• Dolby Digital (also called AC-3): A surround encoding format developed by Dolby
Laboratories that contains up to six discrete audio channels. Although typically used
to encode every channel of 5.1 surround, it can also be used to encode any subset of
these channels. Compressor is capable of encoding any combination of up to five
appropriately mixed audio channels plus a sixth LFE channel into a Dolby Digital audio
file that you can use for authoring DVD Studio Pro projects. For more information, see
the Compressor and DVD Studio Pro documentation.
• Dolby EX: Another surround encoding format, designed to accommodate 5.1, 6.1, or
7.1 channels within the same bandwidth. Encoding any channels above 5.1 requires
matrixing to fit an additional center channel and/or rear surround channel into the
same data space. As a result, the additional channels are not discrete channels, and
additional decoding hardware and speakers are required to make use of them.
• Dolby E: A surround format that allows up to eight audio channels to be encoded as a
digital stream that can be recorded onto an ordinary pair of audio tracks, enabling 5.1
surround mixes to be output to nearly any tape format capable of recording at least
16-bit audio. (6.1 and 7.1 mixes require the tape format to be capable of 20-bit
recording.) Dolby E should not be played without being routed through an encoder. The
encoded digital signal is not intelligible (at least, not to human ears) and may damage
your audio equipment. Dolby E requires special equipment for encoding. However,
once encoded, Dolby E audio tracks may be output to tape using Final Cut Studio the
same as any other pair of audio tracks.
• Digital Theater System (DTS): Another family of digital surround formats that compete
with Dolby Digital. DTS requires third-party software for encoding (a
Mac OS X–compatible encoder is available from DTS Digital Entertainment). Once
encoded, DTS audio files can be imported by DVD Studio Pro (up to 6.1-channel surround
sound is compatible) and used for DVD authoring. For more information, see the
DVD Studio Pro documentation.
If you’re providing a surround mix for your program, there are a variety of ways that
distributors may ask for it to be delivered.
• Many broadcasters request that all of your surround channels be output discretely to
a digital multitrack tape format. For example, DTRS-format decks are often
recommended, including the Tascam DA-88 and DA-98, each of which records eight
channels of audio with device controllable timecode that you can synchronize to your
master videotape. Typically, a pair of synchronized stereo downmix channels is also
output. When you provide the individual surround mix channels, the audio can be
encoded into any format necessary.
106 Chapter 6 Mastering