Variable log/expo converter

[Martin Czech]

:::From: Toby Paddock <tpaddock at seanet.com>
:::To: "'synth-diy'" <synth-diy at node12b53.a2000.nl>
:::Subject: Variable log/expo converter
:::Date: Sat, 22 Apr 2000 10:06:06 -0700
:::
:::Is there a fairly simple circuit (don't laugh) that can be adjusted to 
:::go from log to linear to exponential? Set by a pot or CV? 
:::The tiny bit I understand about log/expo circuits 
:::makes me guess NO, but you never know till you ask.
:::I was thinking of using it to change the response curve 
:::of a non-keyboard CV controller. Change the "feel".
:::It would not have to be very accurate, or thermally stable 
:::because it would no need to accurately scale a VCO.
:::
:::Actually, the function y=x^m, where m is adjustable might be better.
:::I can see using a multiplier that you put x into both inputs and get x^2.
:::Put x into one input and "1" into the other will give an output of x^1 or
:::linear.
:::An m of 0.5 would be square root, but it's beyond me how to do that 
:::or how to make it variable. 
:::
:::Does this even make sense?


I think this is the typical case where a mathematical nice concept will not be
very usefull in practise nor economic. I could imagine that for the "feel" of
a controller something very crude could be sufficient, if you are not
a very sensitive person. Exceptions are possible , however.

Inverting op-amp gain stage, input resistor replaced with diode?
Fairly exponential. Series resistor will make it more linear.

m.c.