The Technical Stuff
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24
great, results in virtually no increase in output level. Note that the 6176 has been designed so that
selecting higher ratios also raises the threshold level.
As an aside, an
expander
is the opposite of a compressor: a device which
increases
the dynamic
range of a signal. For example, a 10 dB change in the input signal might result in a 20 dB change in
the output signal, thus “expanding” the dynamic range.
Knee
A compressor's
knee
determines whether the device will reach maximum gain reduction quickly or
slowly. A gradual transition (“soft knee”) from no response to full gain reduction will provide a
gentler, smoother sound, while a more rapid transition (“hard knee”) will give an abrupt “slam” to
the signal. The 6176 utilizes soft knee compression and limiting, which is generally preferred for
most musical applications; hard knee compression or limiting is more often used in applications
where instrumentation (such as broadcast transmitter towers) must be protected from transient signal
overloads.
Attack and Release
The main key to the sonic imprint of any limiter or compressor lies in its
attack
and
release
times;
these are the parameters which most affect how “tight” or how “open” the sound will be after gain
reduction. The attack time describes the amount of time it takes the limiter/compressor circuitry to
react to and reduce the gain of the incoming signal, usually given in thousandths of a second
(milliseconds) or even millionths of a second (microseconds). A fast attack kicks in almost
immediately and catches transient signals of very brief duration (such as the beater hit of a kick drum
or the pluck of a string), reducing their level and thus “softening” the sound. A slow attack time
allows transients to pass through unscathed before compression begins on the rest of the signal.
The release time is the time it takes for the signal to then return to its initial (pre-compressed) level.
If the release time is too short, “pumping” and “breathing” artifacts can occur, due to the rapid rise
of background noise as the gain is restored. If the release time is too long, however, a loud section
of the program may cause gain reduction that persists through a soft section, making the soft section
inaudible.
In the 6176, both the attack and release times are user-selectable. Attack time can be set to between
20 microseconds and 800 microseconds; release time can be set to between 50 milliseconds and
1100 milliseconds (1.1 seconds). Unlike many other devices, however, the 6176 Attack and Release
times get faster, not slower, as their corresponding knobs are turned up (clockwise).
