optical limiter problem

[media at mail1.nai.net]

>>Because of the very nonlinear R / I characteristic of a vactrol, I have
>>to use a feedback
>>rather than a forward compressor topology. So I have a feedback loop,
>.......problems......
>>Any ideas ?
>
>....well you might do away with the feedback loop by using that system
>I last saw in Elektor 6 months ago, where you have two hopefully similar
>quasi linear optocouplers.... one is forced by feedback to give a linear
>response, and the other carries the signal. so you hope the nonlinearities
>cancel out, which for your purposes I think they will.
>this is a horrible description, but it WAS in Elektor under a heading like
>'linear optocoupler'

Perhaps I misunderstood Juergen's problem.  As I understood it he wanted
the non-linear response of an optocoupler but he was getting this ripple,
and when he tried adding an RC filter he got a resonance that was even
worse.

Then again, I still don't know what he means by "elkos."

>>Firstly, their release time is often too slow.  Secondly, their attack time
>>is also too slow -- really hard transients can still pass through.  In many
>
>depending on your program source, you can make a parallel track which is
>timeshifted (easy in digital editing systems) and use this 'pre delay'
>track to
>run the control of the compressor.....you can get attack times of minus up
>to several hours this way, is that fast enough for you? ;)

No, it would be much too late :)  He wants to limit the signal before it
gets onto the tape.  Once you have it in the digital realm you have
numerous look-ahead limiters to choose from without having to make a
parallel track (although people have actually done that to go from digital
to varigroove).

What I meant to say is that optical limiters don't have the response needed
in front of a DAT or a XMTR.  Of course you could just set it back a little
to compensate for overshoot -- but that almost defeats the purpose of
having a brick-wall limiter.

> Experimental Musical Instruments Journal

Now that sounds interesting. Where is this journal published??  I'd like to
find out more about it.

PEACE OUT :)
MARK