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This system is being gradually phased out in favor of Dolby Digital,
or AC-3, which encodes "5.1" distinct full channels of sound - 1
channel for each of the same 5 speakers used in the older Pro Logic
plus a ".1" channel which contains only deep bass and is intended to
drive a subwoofer. This provides a very compelling sound field when
properly implemented with good quality speakers, since all 5 main
speakers can play independant full-range sounds.

There are also a variety of methods which claim to reproduce an entire
sound field with only 2 speakers or normal stereo headphones. The most
popular of these is "QSound", which has the added advantage of also
being compatible with Pro Logic, so you can get 'real' multi-plane
sound if you've got it and a reasonable imitation otherwise. QSound
was first commercially used for Madonna's "Immaculate Collection"
album, and is now used in arcade, console, and PC-based video games as
well as many other places.

Note that although Pro Logic encoding is possible in realtime on the
IIgs, no known software actually does this. Additionally, the
psychoacoustic methods such as QSound simply require too much DSP
power to pull off in realtime on the IIgs or other Apple II computers,
so be wary of any claims of such. It's certainly possible to
pre-process waveforms with QSound and simulate realtime encoding -
this method is used on systems such as the Sony Playstation which
don't have spare DSP capacity. This "cheat" may or may not work with
other psychoacoustic systems - it depends on the specific coding
method. As always, let your ears be your guide...

_________________________________________________________________

Copyright (c) 1993-1997 Ian Schmidt. Contents may be freely
distributed as long as no editing occurs without permission, and no
money is exchanged. Exceptions are hereby explicitly provided for Joe
Kohn's Shareware Solutions II, the services GEnie and Delphi, for the
current Apple II FAQ maintainer (Nathan Mates), and for user groups
everywhere.
The Apple II: It just keeps going and going and going....