In article ,
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Robert Orban wrote:

says...
Robert Orban wrote:
says...

Thanks Bob !

Him being the one who will be criticised on other groups for making DAB
and FM ever more distorted;!...

All modern DSP-based Optimods can be operated as exremely pure
protection
limiters if that is what the broadcaster prefers, and we offer presets
to
make this easy. I just make the artillery; I don't have any say in how
broadcasters choose to set it up!

BTW, did you ever use 'optical' compression ? Vactrols etc.

Only once, for a cue amplifier in a one-off broadcast console I built in
the late '60s for a friend's radio station. I drove the lamp from the
output
of the cue power amplifier, which made the compressor very cost-effective.

Optical compressors are very interesting because of their complex, program-
dependent attack and release times. However, IMO they are not adequately
repeatable in a mass-production environment, so I never seriously
considered
using them commercially.

One of my competitors did (in a four-band processor) and it caused him and
his customers no end of grief with unit-to-unit consistency problems and
temperature sensitivity.

I had them selected by Silonex and we had no such problems.
http://www1.silonex.com/

Their characteristics are indeed very interesting and seeming inherently
suited
to music. My first use of them was in a mixer-amplifier to avoid accidental
serious overload. Tuning the time constants you could move the master fader
from
'-5' where the amp was briefly clipping (largely inaudibly) to '+5' and you
could whizz the fader back and forth between the 2 points and the sound was
almost completely unaffected. It was as if you weren't doing anything ! It
would
allow ~ 1% THD on tone and then cut-in.

More lately we used a Chinese device. Less consistent so required more
selection
into grades and the fitting of grade dependent Rs on the control board. 1/8th
the price though.

I forgot to mention that we at Orban have had substantial experience with
optos, but not for use with compressors. In the mid 80s, we did some R&D for a
digitally controlled analog parameteric EQ that used optos as the
variable resistance elements for adjusting Fc, BW, and gain. We used dual
optos driven by a single lamp, with one side handling the program audio and
the other side having DC applied to it to close a servo feedback loop. This
made the control law predictable and stable. We relied on close matching of
the two sections of the opto, particularly over temperature.

Because the optos had too much soft nonlinearity to produce state of the art
distortion measurements, we eventually dumped them and ended up going with
MDACs even though the latter caused audible glitching when the controls were
operated, unlike the optos, which sounded completely smooth. But the MDACs
were much more linear.