Owner`s manual

Dynamics Processors
378
Appendix
Compressor
A compressor provides a form of automatic level control. By attenuating high
levels, thus effectively reducing the dynamic range, the compressor makes it
much easier to control signals and set appropriate fader levels. Reducing the
dynamic range also means that recording levels can be set higher, therefore
improving the signal-to-noise performance.
Compressor (CMP) parameters:
Threshold determines the level of input signal required to trigger the compres-
sor. Signals at a level below the threshold pass through unaffected. Signals at
and above the threshold level are compressed by the amount specified using
the Ratio parameter. The trigger signal is determined using the KEY IN parame-
ter.
Ratio controls the amount of compression—the change in output signal level
relative to change in input signal level. With a 2:1 ratio, for example, a 10 dB
change in input level (above the threshold) results in a 5 dB change in output
level. For a 5:1 ratio, a 10 dB change in input level (above the threshold) results
in a 2 dB change in output level.
Attack controls how soon the signal is compressed once the compressor has
been triggered. With a fast attack time, the signal is compressed almost immedi-
ately. With a slow attack time, the initial transient of a sound passes through
unaffected.
Out Gain sets the compressor’s output signal level. Compression tends to
reduce the average signal level. Out Gain can be used to counter this level
reduction and set an appropriate level for the next stage in the audio path.
Knee sets the transition of the signal at the threshold. With a hard knee, the tran-
sition between uncompressed and compressed signal is immediate. With the
softest knee, knee5, the transition starts before the signal reaches the threshold
and gradually ends above the threshold.
Release determines how soon the compressor returns to its normal gain once
the trigger signal level drops below the threshold. If the release time is too short,
the gain will recover too quickly causing level pumping—noticeable gain fluc-
tuations. If it is set too long, the compressor may not have time to recover before
the next high level signal appears, and it will be compressed incorrectly.
Parameter Value
Threshold (dB) –54 to 0 (55 points)
Ratio 1.0, 1.1, 1.3, 1.5, 1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0, 8.0,
10, 20, ∞ (16 points)
Attack (ms) 0 to 120 (121 points)
Outgain (dB) 0 to +18 (36 points)
Knee hard,1,2,3,4,5 (6 points)
Release (ms) 5 ms to 42.3 sec
*1
, 6 ms to 46.0 sec
*2
, 8 ms to 63.4 sec
*3
(160 points)
*1. These values are obtained when the sampling frequency is 48 kHz.
*2. These values are obtained when the sampling frequency is 44.1 kHz.
*3. These values are obtained when the sampling frequency is 32 kHz
-70
-60
-50
-40
-30
-20
-10
0
+10
+20
-70 -60 -50 -40 -30 -20 -10 0 +10 +20
Input Level
Output Level
dB
dB
Knee = hard
Threshold = -20dB
Compression ratio = 2:1