Attack, Release And Ratio - BSS Audio DPR 404 User Manual

Comparing the input and output waveforms for the compressed mode, the
loudest portions of the signal have been effectively decreased in level, and if
the gain control is adjusted to compensate for this, the quieter portions will be
increased. The net effect, therefore, is for both ends of the dynamic spectrum
to be pushed (or squeezed) towards each other. This squeezing effect of
compression is important to remember, and provides a major difference
between compression and limiting. I.e. Limiters do not make-up the gain
reduction.
The range provided by the DPR-404 on its ratio and release controls is
sufficient to allow its use either as a compressor or limiter. For limiter
applications, the release fast switch should generally be out.
Attack is the amount of time that elapses before the compressor begins to
11.2 Attack,
attenuate the output level after the threshold point has been exceeded. For
Release and Ratio
sounds such as a snare drum or hand clap, fast attack is desirable so that the
compressor responds in time to control the peaks.
Release is the amount of time taken for the compressor to return to normal
gain after the input signal has fallen BELOW the threshold point.
Ratio determines the ratio of change on output level to changes in input level
for all signals that exceed the threshold. Returning to section 1.1 where the
idea of manual controlling the level of the program was discussed, the
operator would reach over and turn down the volume if signal levels were
approaching distortion. At this point he now has an option: Either reduce the
level so that there is nothing exceeding his desired maximum level, or reduce
the level by a small amount so that his output is slightly greater than that of
his preferred maximum but not as loud as it would have been if no action had
been taken. This action is known as the ratio. A ratio of 1:1 indicates that the
output will linearly track the input level of the threshold. i.e. For every 1dB of
input over the threshold point, there will be 1dB of output. A ratio of 2:1
indicates that for every 2dB of input level above the threshold, there will be a
corresponding increase of 1dB in the output level. A ratio of 10:1 indicates
that for every increase of 10dB of input level, there will be a corresponding
increase of 1dB in the output level, and so on. A ratio of infinity:1 indicates
that no matter how loud the input signal goes above the threshold, the output
will remain constant at the threshold point. It is worth noting that a hard or
infinite ratio limit has applications in some specialised situations, but in
general it is neither appropriate nor necessary, and is likely to cause noticable
side effects in the sound.
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