Lexicon NUVERB - FOR MACINTOSH Manual page 109

NuVerb User Guide
Reference
Compressor
General Description
The Compressor effect is a true digital compressor which will run in either Dual Mono or
Cascade mode. In Dual Mono mode, it configures to Mono in Mono out; in Cascade mode, it
configures as a true stereo effect. The compressor can be described as an upwards averaging
compressor. Digital compressors, like analog compressors, decrease audio above a given
threshold. Unlike analog compressors, they increase gain below the threshold. The result from
either analog or digital compression is exactly the same — less dynamic range.
The audio path takes two routes. One path goes through a predelay mechanism which delays
the audio a maximum of 48 ms. The other path sends control information (dependent on the
CmpGain and ExpGain. As the signal crosses the threshold point, both Compressor Gain and
Expansion Gain vary constantly. Compressor Gain determines the maximum amount of gain
increase below the threshold; Expansion Gain determines the maximum amount of gain
attenuation below the threshold.
Generally, digital compression requires lower threshold settings than analog compression.
The reason for this is that there is no such thing as headroom in a digital system — dBfs (Digital
Full scale [0VU]) is the maximum level audio. Audio dynamics below full scale, however, can
be manipulated and modified.
The whole purpose of a digital compressor is to maintain peaks while compressing lower level
audio signals upwards. If you think about it in terms of the most significant and least significant
bits, you would never want to reduce the most significant bits — you want to increase the least
significant bits.
Adding some predelay gives the control mechanism time to react before the audio reaches the
digital VCA. Of course, the more predelay you add, the more "out of sync" the audio will
become. Attack constants should be kept to short values (7,15, or 30ms). A good starting point
for release time is 91 or 114 ms.
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