Dolby Laboratories 585 - Manual (Page 9)

Model 585 Time Scaling Processor
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Chapter 1
Introduction
The Model 585 Time Scaling Processor delivers true time scaling and pitch shifting
for the studio professional.
A change in the playback speed of analog tape—or in the sample playback rate for
digital formats—has always brought about a change in the audio pitch as well as the
duration of the audio program being played. However, this fixed link between
playback speed and pitch has often meant a compromise in audio quality. Therefore,
the ability to precisely determine and alter pitch and program duration independently
has been a necessity since it first became possible to alter the speed of a recording.
Today, many standard operations result in a change in audio pitch; for example, when
converting a film for broadcast at 25 fps, or adjusting a program’s length to match the
available broadcast time slot.
There have been attempts over the years to provide pitch shifting and time scaling.
Early products showed glaring weaknesses, and more recent attempts have tended to
be useful only on a limited range of material. Model 585 delivers dependable
processing of any signal, across the whole spectrum of audio: music, speech, special
effects, and any combination of these elements.
Multichannel Delivery
Model 585 is the first product to deliver truly phase-synchronous time scaling and
pitch shifting for multiple (up to eight) channels of audio—something multiple stereo
processors cannot achieve. It is important to preserve the phase relationship of
multichannel audio programs for all listeners; it is especially important for those with
stereo or mono reproduction equipment, who hear a summing of the multichannel
elements. Model 585 is compatible with all Dolby
® E products.
Real-Time Time Scaling and Pitch Shifting
Model 585 delivers two separate functions: time scaling and pitch shifting. Each
function can be applied in real time.
Time scaling alters the duration of an audio signal but leaves the perceived pitch
unchanged from the original signal. Time scaling and how to implement it using
Model 585 is discussed in Chapter 3.