Yamaha GC2020C - Manual (Page 5)

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Compressor/Limiter Parameters
GC2020C Compressor/Limiter Owner’s Manual
Compressor/Limiter Parameters
Threshold Level
Threshold is the signal level at which compression or limit-
ing begins. All signals below the set threshold level are
passed as received at the INPUT jacks, with no compression
or limiting applied. Signals going above the set threshold
level, however, are compressed or limited according to the
settings of the RATIO, ATTACK, and RELEASE controls.
Ratio
This is the amount of compression applied to signals that
exceed the threshold level set by the THRESHOLD control.
The compression ratio is expressed in terms of the amount
of change in the level of the input signal in relation to the
corresponding amount of change in the level of the output
signal. A high ratio means a lot of compression. A compres-
sion ratio of 1:1, therefore, implies no compression—a
change of 1 in the level of the input signal produces a corre-
sponding change of 1 in the level of the output signal. A
compression ratio of 2:1, however, means that for a given
change in the level of the input signal (2) the level of the out-
put signal will only change half as much (1). The extreme
would be a compression ratio of
∞
:1 (infinity to one), mean-
ing that no matter how much the input signal level changes
the output signal level will remain constant. The
∞
:1 com-
pression ratio is most commonly used in hard limiting
applications where the signal level must be prevented from
exceeding a specific value (frequently 0 dB). Extremely high
compression ratios in the range of 20:1 can add sustain to
instrument sounds—especially electric guitar and bass—as
well as creating a contemporary drum sound. Lower com-
pression ratios—from less than 2:1 to 8:1—are useful for
making vocals sound smoother and minimizing the level
variations that occur when a speaker or singer moves closer
to or further away from a microphone.
Figure 3
Attack Time
The Attack Time determines how long it takes—in millisec-
onds—before the full amount of compression is applied
once the threshold level is exceeded. The ATTACK time
range is from 0.2 milliseconds, a very fast attack, to a rela-
tively slow 20 milliseconds.
The attack time setting depends largely on the type of signal
being processed and the type of effect desired. A very fast
attack, for example, will compress the initial attack of an
instrumental note making it sound “dull”. High levels of
compression are sometimes used on electric guitar, for
example, to give the sound greater sustain. In this applica-
tion it is often better to set a longer attack time so that the
crisp attack of the guitar note “gets through” before full
compression is applied. Set the attack time to accommodate
the natural attack of the sound being processed.
Figure 4
+30
+20
+10
0
–10
–20
–30
–40
–50
Threshold level
Output Signal Level (dB)
Intput Signal Level (dB)
COMPRESSION RATIOS
–60 –70 +30 –50 –40 –30 –20 –10 0 +10 +20
1:1
2:1
4:1
8:1
20:1
:1
Attack Time set to zero
Input Signal
Fast Attack Time
Attack Time
Slow Attack Time
Attack Time
ATTACK TIME Control Function