30
Sabine Smart Spectrum
®
Wireless
© 2011 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 (typically 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 dynamic
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. Compression 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 compressor 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 Compres-
sor.
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 compression
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
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