E Q / D Y N A M I C S S E C T I O N
page 16
D-12 / July 2006
Compressor/Limiter
The compressor algorithm used in the D-12
control surface is designed to:
- allow smooth, inaudible, and unobtrusive
level control on uneven sources;
- be able to act as a peak limiter for inadvert-
ent overload control;
- enable deep effects if required.
The compressor section is a compound of
many diverse dynamics elements.
The level detector is a pseudo-RMS averag-
ing type with its own symmetrical-in-time attack-and-release characteris-
tic adjustable between 0.1mS and 330mS (“Attack” control). At the slower
end of its range, by itself it achieves a nouveau-classic “dbx” style syllabic-
rate level control. As the time-constant is shortened, it becomes progres-
sively shorter in relation to the lower audio frequencies themselves; the
effect is to turn the detector into more of a peak-level detector, necessary
for limiting or wilder effects. A secondary effect at intermediate to fast
attack-times is that low frequencies are peak sensed while high frequen-
cies are average sensed resulting in an effective high-frequency bias (up
to as much as 6dB differential) which helps to mitigate the detrimental
limiting effect of the resulting audio seeming “bottom heavy” normal to
most compressors.
While the overall gain-reduction scheme is “feed-forward”, the heart
of the detector stage itself is a feedback limiter; this allows for this
carefully-contrived loosely-damped servo-loop to permit far more inter-
esting dynamic effects.
The compressor is “soft-knee”, meaning the compression ratio in-
creases slowly with increasing applied level, greatly easing the sonic
transition into full compression; it helps avoid the “snatching” and
“pumping” at threshold that many “hard-knee” dynamics units exhibit.
A full range of controls is available over the compressor’s behavior:
Threshold
The THRES knob sets the level at which the compressor is fully into
compression of whatever ratio is set. This can be set anywhere in the range
of -30dB to +10dB, unless the lower range is limited by the GATE THRES
setting (see below).
Attack
This control determines how quickly (between nominally 0.1mS and
330mS) the compressor reacts to signals. Faster attack times result in
“tighter” and more obvious control; longer attack times lend themselves
well to gentler automatic volume control.
