[linux-audio-dev] Rectifier algorithm and Exponential FM question

[nickt]

>   out = sin(exp(freq))
That's my guess. I know ALSA Modular has Exponential FM, but I have not
found out where is doing it or how. 

My guess is that an exponential jack does something similar like this
and than passes it to circuit for modulation. So it might do something
like exp(signal).

The signal itself is modulated between 1 octave down and 1 octave up. 
A straight exp(x) will not do that. It has to be a formula of some sort.