User's Manual

30
Sabine 2.4 GHz Smart Spectrum
®
Wireless
8.4. Possible Compression Trouble Areas
Like any signal processing, compression can be misused, and improper
application 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 prob-
lem will be exaggerated 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 thresh-
old 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 some-
times 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 dynamics, 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 . Re-
lease time adjusts the speed with which compression stops and output gain
returns to unity with input gain, once the input signal falls below the compres-
sion threshold. Knee refers to the degree with which the full ratio of compres-
sion is imposed once the input level threshold is approached and exceeded.
A “hard knee” changes from no compression to maximum compression ex-
actly and immediately at the threshold crossing; a “soft knee” gradually im-
poses 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
TM
Remote Software (see Section 13 for details).
Compressor Limiter