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D - 8 G U I
page 28
D-8 / Feb 2009
The controls are:
EXP IN — A switch that allows the expander to be enabled and disabled.
THRESHOLD (-60.0dB - 0.0dB) — Below which the automatic attenua-
tion starts to take effect.
RATIO (1:1.0 - 1:5.0) — Being the proportion of how many dB the input
signal is attenuated for every dB it drops below the threshold. 1:3 indicates
18dB loss for 6dB drop in input signal level.
DEPTH (0.0dB - 40.0dB) — The maximum amount the expander is
permitted to reduce the input signal level.
OPEN (1.00mS - 100.0mS) — The time-constant of the rate at which the
expander un-attenuates, or opens; sometimes called “attack”.
HANG (0.00mS - 1.000S) — An adjustable period of time the expander
remains open without attenuating, before starting to close. Handy to keep the
expander open during, say, speech inter-syllables or other short pauses,
without having to resort to excessively long...
CLOSE (50.0mS - 3.000S) — ... close times, being the rate at which the
expander attenuates away the input signal once below the threshold.
An input/output plot, a graphical representation of the relationships be-
tween threshold, ratio, and depth, is seen on the Expander Control screen of the
GUI. It is a handy visual aid.
Almost always, the trick is to set the threshold of the expander - below
which it starts to attenuate away the input signal - high enough to capture the
noise, but not too high as to snatch at the lower levels of the desired parts of the
program material. That can sound really irritating.
Sometimes the gain reduction is required to be subtle so as not to draw
attention to the fact that the expander is in operation. Under these conditions
shallow expansion ratios, such as 1:1.5 or 1:2 are preferred, as are restricted
depth - 6dB, or 10dB, is plenty and makes a substantial subjective improvement
to the noise.
These, too, are the kind of settings used for another application of an
expander, that of effectively shortening an excessively long room reverbera-
tion time, or an instrument’s ring-out that is overly persistent. In these cases the
threshold is set somewhat higher, well up into the desired audio levels - in this
way the attenuation becomes part of the overall sound, but the gentle ratio
prevents a sense of anything “odd” happening. Again, relatively shallow
depths of 12dB or so are plenty to achieve the desired effect.
More aggressive expansion, or “gating,” is accomplished with steep
ratios (1:3, 1:5) and with shorter open and close times than for “unobtrusive.”
It is still best not to go overboard with depth - even just 14dB, 20dB tops, is
enough to make a signal “disappear” in the context of a mix; the whole gating
sound, especially surprisingly its opening, is less obvious with shallower
depth. Sometimes the “Surprise!” element is required, though, for effect.