Page 144 - The Master Handbook Of Acoustics

CHAPTER
6

Analog and Digital

Signal Processing

n the early days of sound recording, signal storage was a major prob-
Ilem. The final recording was laid down directly, without benefit of
stop-and-go recording of portions that could be patched together later.
This had the advantage of minimizing the number of recording gener-
ations, but the format was a stringent one with little latitude for artis-
tic enhancement.
With the introduction of high-quality signal storage (magnetic tape
or digital memory) many creative decisions, normally reserved for the
recording session, were moved to the mix-down session. This opens
up the opportunity of making quality enhancements in the mix-down
session, long after the recording session is finished and forgotten.
These quality enhancements are often made with filters of one kind or
another. Is there a short traffic rumble on take 6 of the recording? A
high-pass filter might cure it. Did that narrator’s dentures contribute
an occasional high-frequency hiss? Run it through the “de-esser.”
How about that congenital 3 dB sag in the response at 4 kHz? Easy,
add a 3 dB peak of appropriate width with the parametric equalizer,
and so on.
The introduction of integrated circuits in the 1960s made signal
processing equipment lighter, more compact, and less expensive. The
coming of the digital revolution made it possible to routinely accom-
plish sophisticated signal processing tasks, heretofore impractical or
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