On 22 Dec 2006 06:10:17 -0800, "Telstar Electronics"
wrote in
om:

Frank Gilliland wrote:
Well, here's some more techno-babble:

Real-time or feedback type compressors such as the SMM2166 use a
comparator to create the control signal and results in a "knee" in the
response curve. But any curve that has a knee is non-linear and
results in harmonic distortion (same as "compression distortion" in
your RF amps). Because the harmonics extend beyond the limit of your
audio bandwidth you must therefore limit that distortion with filters.
Since filters are non-linear with respect to frequency, and since
audio is an extremely wideband application, some part of the loop
(usually the preamp) must compensate for the diminishing high
frequency response (yes, even when the audio is limited to 3kHz).
That's called "frequency compensation" and is something that must be
included in the design of any compression circuit (or amplifier). You
can try to soften the knee by slowing the response time of the control
signal, but that results in spikes at the output because some of the
signal sneaks through during the time delay. So no matter what you do,
distortion is just an inescapable limitation of these circuits. If you
want to learn more on the subject, get an education.

You're right... your response is nothing but techno babble. You need to
read the complete data sheet for the SSM2166
(http://www.analog.com/UploadedFiles/...s/SSM2166.pdf).


I've had it in my files since the chip first came out. Studied it
several times. Even used the chip in a couple designs.


It
faithfully reproduces an audio sinewave... but has an AGC.


Any linear amplifier will "reproduce" a sinewave. If it has AGC then
how "faithfully" that sinewave is reproduced depends on the time
constant of the AGC loop.


The harmonic
dostortion is less than 1% according to the spec.


That's for a 1kHz sinewave with 1:1 (no) compression. That's pretty
crappy even for a CB, and proves that -you- didn't read the complete
datasheet. For comparison, look at the specs of the CA3080.


So far, my new design
is working well... and has constant audio punch level... no matter if
you whisper or yell into the mic Exactly what is needed!


If that's the case then you set the feedback time constant too slow
and built yourself a CVA, not a compressor. Look at the scope and you
will see spikes.


With the fast
attack/release of the noise gate feature.. this chip is fantastic at
blocking ambient background noise!


Yes, it works very well at blocking signals. So does a switch. The
problems start when it begins -passing- signals. Didn't I tell you to
do your research?