Telex Integrated Signal Processor ISP-100 - Manual (Page 75)

8-5
Processing Components - Compressor
threshold value, no compression takes place and the change in
level of the output signal exactly matches the change in level of
the input signal. When the input signal level is above the
threshold value, compression is used and the change in level of
the output signal is less than the change in level of the input
signal by the amount dictated by the selected compression ratio.
Threshold is adjustable in the range -60 dBFS to 0 dBFS.
Attack Time
A compressor monitors the level of the input signal and controls
the level of the output signal accordingly. When the input signal
level suddenly increases, a compressor allows the output signal
level to also increase, but only as much as is appropriate for the
selected compression ratio setting. Desirable sound effects can
sometimes be created if a compressor is forced to ramp the
output signal level to its new value gradually rather than
instantaneously. The Attack Time control adjusts the duration of
this ramp. Attack Time is adjustable in the range 20
µ
Sec (one
sample) to 50 mSec.
Release Time
A compressor monitors the level of the input signal and controls
the level of the output signal accordingly. When the input signal
level suddenly decreases, a compressor allows the output signal
level to also decrease, but only as much as is appropriate for the
selected compression ratio setting. A compressor generally
sounds better if it is forced to ramp the output signal level to its
new value gradually rather than instantaneously. The Release
Time control adjusts the duration of this ramp. Release Time is
adjustable in the range 20
µ
Sec (one sample) to 5 mSec.
Knee Selection
Below the threshold level, no compression is taking place and
any changes in input level are matched exactly by changes in
output level. Above the threshold level, compression is taking
place and changes in output level are less than the
corresponding changes in input level. The transition from no
compression to compression can be set to take place abruptly or
gradually.
Under hard knee conditions the output level tracks the input level
perfectly as it rises up to the threshold. Above the threshold the
output level continues to rise as dictated by the compression
ratio. There is an abrupt transition from no compression below
the threshold to compression above.
Under soft knee conditions, there is a smooth, gradual transition
from no compression below the threshold to compression above.
Under soft knee conditions the output level and the input level
track until approximately 12-18 dB below the threshold, beyond
which they slowly begin to diverge. Depending upon the
compression ratio selected, the output level may be as much as