The Technical Stuff
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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 LA-610 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 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 compression.
The attack time describes the amount of time it takes the compressor circuitry to react to and reduce
the gain of the incoming signal, usually given in thousandths of a second (milliseconds). The LA-610
attack time is approximately 10 milliseconds (though, like ratio, this is somewhat program
dependent). A fast attack such as this 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. Like its predecessor, the LA-2A,
the LA-610 is unique in that it provides a dual stage release time: in the first 60 milliseconds,
approximately half the signal is released, with the remainder taking anywhere from 1 second to 15
seconds to die away, depending upon its frequency content.
Makeup Gain
Finally, an output control is employed to make up for the gain reduction applied by the gain reduction
circuitry. Makeup gain is generally set so that the compressed signal is raised to the point at which it
matches the level of the unprocessed input signal (for example, if a signal is being reduced in level
by approximately -6 dB, the output makeup gain should be set to +6 dB).
As you are adjusting a compressor, a switchable meter such as the one provided by the LA-610 can be
helpful in order to view the strength of the incoming signal (displayed when the meter is set to
PREAMP), the strength of the outgoing, post-compression signal (displayed when the meter is set to
COMP), or the gain reduction fluctuations as they occur (displayed when the meter is set to GR). When
in COMP mode, the LA-610 meter will read 0 dB when there is no incoming signal or when no
compression is being applied.
