Specifications

Chapter 30: Surround Concepts 505
Surround Formats and Delivery
Mediums
Surround mixes are tailored for their specific de-
livery medium. Most often, this requires format-
specific encode and decode processing.
Encoding and Decoding
Many surround formats utilize some form of en-
coding and decoding to make it practical to de-
liver, broadcast, and transfer the multiple chan-
nels of full-bandwidth audio they require.
◆ Encoding is the process necessary to make mul-
tichannel mixes portable and playable. In many
cases, this involves taking the four, five, six, or
more discrete channels resulting from a multi-
channel mix and converting them into a two-
channel stream for broadcast (still a predomi-
nantly 2-channel medium).
◆ Decoding is the process needed to reproduce
(or unfold) the discrete surround channels from
a 2-channel delivery medium.
Both encoding and decoding, no matter how re-
fined, represent additional processing stages ap-
plied to your mix before it reaches its ultimate
destination, the audience.
For example, because the Dolby Surround algo-
rithm depends heavily on phase relationships,
there is always a significant difference in a de-
coded LCRS output as compared to the original
LCRS mix. To account for these anomalies, engi-
neers mixing for Dolby Surround listen through
hardware encode and decode processors for ref-
erence.
Professional mixing and mastering engineers
use encoders and decoders to precisely audition
the effect of the encoding and decoding process,
and make any adjustments necessary.
Surround Processing and Pro Tools
Pro Tools requires additional software or hard-
ware for surround encoding, decoding, and pro-
cessing. For example, the Dolby Surround
Tools
™
plug-in lets you monitor and process
completely within the Pro Tools environment.
Surround Tools and other surround processing
solutions are available from Digidesign and
third party manufacturers. Contact your Digide-
sign Dealer for more information.
Surround Playback System
Variables
Different playback systems for surround sound
introduce varying amounts and types of filter-
ing, bass management, and other variables.
These include the specifications for certain sur-
round formats, as well as options to fine-tune a
system for its particular installation.
In your own studio, you know what speakers
you are listening to, what their qualities are, and
what your control room sounds like. What is
impossible to know, however, is what speakers
are in the living room, theater, or concert hall
where your mix will be heard by an audience.
Some delivery media on which surround for-
mats are distributed may have additional
audio constraints, which could influence
your work flow in Pro Tools. Dolby Digital
audio on a DVD-Video disc, for example,
requires a 48 kHz sampling rate. If your
Pro Tools session isn't at 48 kHz, you must
sample rate convert the audio before encod-
ing it with Dolby Digital for DVD.