LA Audio BCL20 - Manual (Page 10)

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compressor ONLY acts upon those frequencies and passes all
other ones.
GENERAL GENERAL
The usual purpose of Limiting and Compression is to increase
loudness and to provide overload protection and generally to
control level.
Limiting Limiting
Limiting is used mainly to provide overload protection ; i.e. to
limit the output to some desired output level.
The protection required is usually against transients which
exceed the peak input level required for a tape recorder or a
transmitter.These high energy transients are usually of very
short duration (micro-seconds) but may wreck a transmitter or
ruin a good recording by introducing distortion.
Control of these transients by limiting does not noticeably affect
the dynamic range, since the gain reduction, when it does occur,
is momentary and of a relatively low order of magnitude. In most
cases, a fast release time will be employed so that the transients
are controlled quickly without any apparent change in
programme content.This form of compression, using ratios of
10:1 and above allows the engineer to reduce his system
headroom, and operate with a higher recording or broadcast
level without fear of overload and thus increase the useable
dynamic range of a recording or transmission system.
Compression Compression
Compression describes conditions of gain reduction that are
more or less continuous, so that the original dynamics are
compressed. A low compression ratio is used when it is
desirable to preserve a relationship with the original dynamics,
but higher ratios provide useful effects, particularly in "pop"
recording and the transmission of speech, where the main
sound source needs to be brought out clearly. This is effectively
increasing the loudness of the signal, and this enhances its
prescence in a recording or over a background.
Attack and Release time Attack and Release time
Attack and release times are important when using
compression, since they determine the moment to moment gain
change in a system, and therefore the apparent loudness. A fast
release time combined with a high ratio will bring more of the
lower level signal content up towards peak level, and a fast
attack time will really bring out the prescence. However, this
kind of setting can sometimes be heard to be "breathing" or
"pumping". This is the effect where the main sound source is
intermittent and you notice the compressor working. (Suddenly
the main voice comes through and sounds veryfull, and then as
it pauses, the compressor turns off, allowing the back-
ground noise to be heard, and then the voice cuts in again
immediately obscuring the background). In these cases it may