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Sabine 2.4 GHz Smart Spectrum
®
Wireless
© 2007 Sabine, Inc.
8. COMPRESSOR/LIMITER OPERATION
8.1. Basics of Compression
The dynamic range (how loud we can hear to how quiet a sound we can detect)
of the human ear is far greater than the capability of sound systems to repro-
duce. Although some of this equipment limitation is at the upper extreme of the
dynamic range (where too loud a signal will produce distortion), much of the
restriction occurs at the low level end, where the signal disappears below the
“noise floor” of the circuitry.
A compressor (or in its most powerful form, a limiter) is the most widely used
tool for controlling dynamic range. In the simplest terms, a compressor is
designed to squeeze the dynamic range of an audio program; i.e., to make
quiet signals louder, and loud signals quieter. A compressor becomes a
limiter when the compression ratio (the ratio of the input gain change to the
output gain change) is so high that the output level effectively won’t rise above
a “brick wall” ceiling, regardless of how much the input gain increases (typi-
cally a ratio of 10:1 and greater).
A compressor acts like an “automatic mix engineer” with a hand on the fader
and an inhumanly fast reaction time. When the input level increases, the
“engineer” drops the fader; when the level decreases, the fader is raised.
When the amount of fader compensation equals the variation in signal level,
the output level of the audio program will sound consistent.
The practical benefits of compression and limiting include:
1. Speaker protection. A compressor will control sudden level peaks and
prevent your speakers from damage. Most often in this type of application,
the compression ratio is high enough to qualify as a limiter.
2. Perceived increase in loudness. Because compressed peak levels are
kept from rising as high as uncompressed signals, you gain headroom for
your audio program and can raise its overall average gain. Compression
is often added to the entire audio mix, both in live sound and recording, to
increase its perceived loudness.
3. Achieving more consistent levels. For expressive instruments or vocals,
which may have a large dynamic range, compression can help maintain
more consistent mix levels. So a speaker who varies from a whisper to a
shout will not disappear or stand out in the mix, relative to other less dy-
namic instruments or vocals. Vocal level variations are also common
when multiple users share a single microphone, due to differences in
voice volumes and mic-to-mouth positions from one user to another. Com-
pression will help even out such variations as well.
8.2. Using the Compressor
Compressor knobs are located immediately to the right of the FBX and De-
Esser controls. The controls consist of standard Ratio, Thresh (threshold) and
Attack knobs, and a horizontal gain ladder in the LED display shows compres-
sor gain reduction.
Ratio:
Compression ratio is the ratio of the input gain change to the output
gain change. The compression ratio on your Sabine Wireless ranges
from 1:1 to 19:1, in increments of 1 dB. Set Ratio to 1:1 to bypass
Compressor.
Thresh: Compression threshold sets the input level at which the compressor/
limiter begins to act on the signal. The input level threshold at which
compression is engaged can be adjusted from -30 dBv to 0 dBv, in
increments of 1 dBv.
Attack: Compressor attack time sets the speed with which signal compres-
sion begins once an input signal exceeds the threshold level. The
range may be adjusted from 1 to 99 mS, in 1 mS increments.
Compressor Limiter
