AW: [sdiy] Dual Frequency Shifter using a log amp

[jhaible at debitel.net]

Ok, I see. The whole thing was a slight misunderstanding.
The nonlinear compression works on channels with fairly
constant amplitude and fairly constant phase. But surely not
for a FS. Not even for a simple phase shifter.

BTW, a phase shifter (APF) has unity gain for any sine shaped input
signal. But it can have severe overshot for other signals which
conatin a mix of tones. I remember I asked on the list some while
ago whether there's an upper limit for the amplitude at the output
of a phase shifter, with an arbitrary input signal of, say, 1V peak
input signal. The answer I got is that there is no limit (!) for
the output signal without making further constraints. (I haven't
investigated further - I just quote this from memory.)
I guess that's why the Moog Phaser derives the min and max voltage
from each of its 12 stages in order to control the overload LED.

JH.

> > I just say sometimes I'm blind, and as I understood Tim has a solution
> > that has worked in practice.
> 
> Only the log function. I haven't put a log signal through a phaser yet. My
> solution was to
> address the compander requirement.
> 
> > Anyway. Compander will work. I have a compander in my old FS-1.
> > A very simple one, too, with long release time constant.
> 
> My log amp has no time component involved, the funtion is approximately:
> 
> sign(input) X post gain X log(abs(input))
> 
> This eliminates the time dependencies of the compander functions.
> 
> Tim Daugard
> AG4GZ 30.4078N 86.6227W Alt: 12 feet above MSL
> http://home.sprintmail.com/~daugard/synth.htm
> 
> 
> 
> 




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