SABINE SWM7000 Operating Manual page 32

Compressor Limiter
Sabine Smart Spectrum ® Wireless
8.4. Possible Compression Trouble Areas
Like any signal processing, compression can be misused, and improper appli-
cation may cause undesirable side effects in the audio signal. Some of these
problems include:
1. Noise. If the threshold for compression is set too low, and the output gain is
raised substantially to make up for the gain loss of compression, the resulting
output signal can be noisy. This is because the overall signal must be raised
significantly to produce the same audible level, and the noise floor of your
equipment will be amplified unnecessarily. This problem will be exagger-
ated if the input signal level to the compressor is very low (which will already
degrade the signal-to-noise ratio).
2. Breathing. In situations where the compression ratio is high, the threshold
is low, and the release time of the compressor is short, the noise floor will
modulate up and down as the audio signal rises above and falls below the
threshold.
3. Over-compression. Applying too much compression to a mix can sometimes
result in such evened-out dynamics that the "life" of the music or speech has
been removed or curtailed. Dynamic variation may be a major component of
a performer's message and command of the audience; don't remove dynam-
ics, just control them. This may be particularly true for percussive musical
instruments such as drums.
8.5. Release & knee Settings
Two other important compressor variables are release time and knee. Release
time adjusts the speed with which compression stops and output gain returns to
unity with input gain, once the input signal falls below the compression threshold.
Knee refers to the degree with which the full ratio of compression is imposed once
the input level threshold is approached and exceeded. A "hard knee" changes
from no compression to maximum compression exactly and immediately at the
threshold crossing; a "soft knee" gradually imposes the full compression ratio as
the input gain approaches and exceeds the threshold. In Sabine products, the
"softness" of a knee can vary from 1-40, with the higher level representing the
"softest" character. In such a setting, slight compression will begin well below
the compression threshold, increase as the input gain crosses the threshold,
and reach full compression well above the nominal threshold.
Values for release time and knee are set at the factory: default release time is
250 mSec, and the default knee setting is a "soft" setting of 20. These defaults
can be temporarily changed or reprogrammed using the Sabine True Mobility
Remote Software (see Section 13 for details).
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