Dolby Laboratories 585 - Manual (Page 35)

Model 585 Time Scaling Processor
6-1
Chapter 6
Principles of Operation
Time scaling of audio has been accomplished previously using a variety of
approaches. Model 585 differs from previous products in two fundamental ways:
•
It provides phase-synchronous multichannel processing in addition to
processing of simpler programs.
•
It steps away from the weaknesses of the various previous approaches.
6.1 Multichannel Delivery
Multichannel audio is now standard in cinemas and is becoming more popular in
broadcast programs as well. For the film, postproduction, and broadcast industries,
time scaling is often necessary, but until now it has required a significant sacrifice in
audio quality.
Model 585 delivers phase-synchronous multichannel time scaling of the highest
quality. Phase-synchronous multichannel processing is essential in today’s
postproduction and broadcast industries because of the variety of replay environments
found in listener’s home. For example, a program broadcast or DVD made in
Dolby
® Digital carries the full 5.1-channel mix along with information that enables
listeners to hear the best 5.1-channel, stereo, or mono mix possible from their audio
setup.
If that same 5.1-channel mix is processed by three two-channel processors set to the
same pitch shifting value, the loss of a common phase relationship between the audio
channels can cause audible problems. The consumer with a complete home theater
system hears six channels that are out-of-phase, while the consumer with a stereo or
mono system hears a severely compromised audio program as the out-of-phase
components are summed together.