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Rev 2.2, 10/31/94
In mastering applications, the de-esser can also be useful to reduce excessive high-frequency
content, for instance, repairing a mix when the cymbals have too much high frequency content
and clutter the high end of the mix.
Set the de-esser by adjusting the
THRESH level until the sibilance is no longer objectionable.
The de-esser and the noise reduction may be used simultaneously. None of the other dynamics
parameters are applicable to the de-esser.
7.5.8 Compression
The compressor generally controls peak levels and maintains a high overall average signal level.
Used in this manner, the compressor's action is generally inaudible. Compressors can also be
used creatively, to make a source sound louder than it really is, or to create a special effect.
For most level control applications, moderate settings yield the best results. We recommend a
starting point of:
THRESH setting sufficient to cause about 6 to 8 dB of gain reduction on peaks
using a
RATIO setting of 4:1. Pick an ATTACK time that allows enough of the initial sound
through to not lose crispness, and a
RELEASE time that allows the compressor to partially
recover (gain reduction display almost out) between words.
For a highly compressed sound (you know, the used car salesman during the 3AM movie), use
a 10:1 ratio setting, 10 dB or more of gain reduction, and a fast release time (fast enough to
cause breathing).
7.5.9 AGC
An AGC (Automatic Gain Control) is simply a smart compressor that knows when to allow its
gain to change. This simple concept allows using a compressor to track a varying audio signal
while maintaining a more constant output level. Note that the goal is to reduce the overall
variation in signal level, not to remove all variation completely.
You set the AGC much like you set the 601's compressor. The big difference is the
THRESH
setting, which becomes the auto-release threshold. This determines the level at which the
compressor allows its gain to rise. (You don't want the gain to rise trying to track a signal
buried in noise, right?) Set the
THRESH so that the lowest desired signal causes fluctuation in
the gain reduction meter.
7.5.10 Downward Expander
The downward expander reduces its gain for any signal level below the threshold setting.
Typically, downward expanders are used to remove noise or unwanted signal from an audio
signal by simply lowering the gain when the overall level falls below threshold.
Think about using the expander when you are faced with a noisy signal (not necessarily hiss) or
when heavily compressing a voice and you want to remove some of the less desirable artifacts
(false teeth rattling, lip smacking, tongue noise, etc.) You can also use the expander to help
remove microphone leakage from a signal.
Start by setting the expansion
RATIO to 1:2. This means that the output falls 2 dB for every 1
dB of below-threshold change in the input signal. Next set the threshold so that the expander
causes gain reduction (right LED meter) as the signal falls in level. Higher expansion ratios will
make the effect more obvious. The
ATTACK parameter determines the expander's response to a
signal's duration; shorter attack times allow the expander to respond to short-duration sounds
(like clicking your tongue). If the attack time is long enough, the expander will ignore short-
duration sounds.
The
RELEASE time parameter determines the length of time needed for the gain to drop once the
input signal abruptly falls below threshold. The
RELEASE time and the expansion RATIO appear
to interact somewhat. This is not the case. A 1:8 expansion ratio means that the output level
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