Frank Gilliland wrote:
One type of compression is "limiting" which either clips or modifies
the dynamic peaks of a signal. Clipping is simply the 'chopping off'
of signal peaks. Limiting can also be done by automatic reduction of
gain as it peaks (a type of automatic gain control). Limiters are used
in radio because dynamic peaks in the audio can cause modulation to
exceed 100% resulting in splatter and distortion. If those peaks are
limited, the average level of the audio signal, and therefore the
"talk-power", can be increased.

Another type of compressor is called a "Constant Volume Amplifier"
(CVA), which uses AGC to keep the level of the signal at a relatively
constant level. (This is different than a limiter because a CVA works
by changing the gain throughout the dynamic range, while a limiter
only reduces the gain at dynamic peaks.) The CVA is used in sound
studios to compensate for changes in the volume of a person's voice
into a microphone. (If you watch reruns of Hee-Haw you can see the
old-timers will adjust their distance to the mic while they sing; they
learned to do this because they often played without the benefit of a
CVA in the sound system.)

Compared to a limiter, the response of a CVA is slow, and cannot be
used to increase the average audio level (talk-power) because it does
not reduce or eliminate the peaks that drive modulation over 100%.

Brian built a CVA.

Well... Frank is almost right... the processor that I'm prototyping has
an VCA (CVA as Frank puts it) amplifier, amplitude limiting, and a
noise gate to cut off unwanted background sound. I suggest you go here
to read for yourself.
http://www.analog.com/UploadedFiles/...ts/SSM2166.pdf

www.telstar-electronics.com