Coding for Transmission and Storage". In the talk, the basic principals of
multi-frequency band perceptual coders will be discussed and related to
the psychoacoustics of the human auditory system. Once this is done,
the basic characteristics of the TDAC transform filter bank used in AC-3
will be examined and the basic operation of the rest of the algorithm
discussed. Particular emphasis will be placed on AC-3 design features
that support multi-channel reproduction in the consumer environment.
AC-3 is interesting in that it has been selected as the US HDTV audio
standard, the 5 channel sound format for Laser Disc, and by Dolby Lab's
for its 5 channel, digital sound format for the Movies.
designing bit rate reduction algorithms. He received a BS. degree in
electrical engineering at Caltech in 1974 and an MS. degree in acoustics
from the UCLA in 1976. From 1978-1984 he was involved in digital-
audio and magnetic recording research at Ampex Corporation. At that
time he became interested in applying psychoacoustics to the design
and analysis of digital-audio conversion systems. Since 1984 he has
worked at Dolby Laboratories and has been involved in the application
of psychoacoustics to the development of audio systems. He currently
is the President and a fellow of the AES.
Thursday, May 18th, 1995 brought the Crown mobile education facility to the Toronto Airport Marriott Hotel. In the capable hands of Doug Bullard from the Technical Support Group, the fifteen members in attendance made a cozy fit into the confines of the Crown semi-trailer. With a glowing wall of amplifiers, the air was positively toasty as Doug got down to the nuts and bolts, or should we say "axons and dendrites" of the IQ System.
Briefly, a Crown amplifier may be fitted with a P.I.P. (Programmable Input Processor) module. These modules come in varying levels of complexity and capability from "dumb" analogue to sophisticated DSP processing with the ability to communicate to other elements and software in the lQ "loop". When mated with IQ matrixers, mixers with ambient sensing capabilities, and the "drone" I/O/logic component, complex system changes and adaptations can be made from many kinds of input data besides operator mouse twitching. The software "brains", available for DOS and Mac platforms, controls such functions as levels, muting, gating, ducking, matrixing, and compression with an easy-to-use-user-configurable GUI. Doug also explained how an amplifier could communicate to the software its operating status, output errors, i.e. - clipping, and even whether the load was within operating parameters. Just the kind of stuff you need to know when operating a very large or even not-so-large system.
In fielding the many questions from the attendees, Doug pointed out that the IQ system will work even in the event of a computer crash - the system configuration stays the same. Of course, knowing how uncommon system crashes are, some people wondered whether the IQ's distributed intelligence design was of any great importance! He also painted a glowing picture of troubleshooting an installation via modem and the IQ network. Heck, why not set the thing up to phone you with a full report if something does go wrong... Now.. if it would only fix itself and bill the client..
In closing, Doug left us with the impression that the uses for Crown's IQ system are limited only by the needs of the venue and the imagination of the designer. System actions and reactions can interface with so many other events in its environment that the word "intelligence" comes to mind. Our thanks to Mr. Bullard and his crew for a glimpse into that future present.
In Kitchener, Paul Reibling.
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