Telex Integrated Signal Processor ISP-100 - Manual (Page 117)

8-47
Processing Components - Limiter
Release Time
A limiter monitors the level of the input signal and controls the
level of the output signal accordingly. When the input signal level
suddenly decreases, a limiter allows the output signal level to
also decrease only as much as is appropriate, given the
relationship between the new input signal level and the threshold
setting. A limiter 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 Sec}.
Knee Selection
Below the threshold level, no limiting is applied and any changes
in input level are matched exactly by changes in output level.
Above the threshold level, limiting is applied and changes in the
output level are not allowed regardless of the input level. The
transition from no limiting to limiting 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 does not change. There is an abrupt transition from
no limiting below the threshold to limiting 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. The output level is
approximately 2.5 dB below the input level at the threshold. The
divergence continues to increase gradually until approximately
6 dB above the threshold, at which point the output level is equal
to the threshold value and beyond which the output level no
longer rises. There is a smooth, gradual transition from no
limiting below the threshold to limiting above.
The sonic differences between the two knee types are often
subtle and are very much signal-dependent. Experimentation is
recommended.
Sidechain Source
There are situations in which limiting is applied to one channel
based upon the level in another channel. This might be used in a
stereo signal pair to prevent image shift; one of the channels
would be considered to be the level reference and the limiters in
both channels would be set up identically.
The Sidechain Source channel selection indicates the channel
whose level is to be used to control the limiter. The choices for
sidechain source are the input channel itself, one other channel,
or the maximum amplitude of these two at any given moment.
This makes stereo linking possible by configuring the limiters
identically and utilizing the same sidechain source for both.