new Formant book arrived

[René Schmitz]

At 03:39 06.11.00 +0100, jh. wrote:

>Maybe it doesn't lock. In OTA polygon filters with 1/1+s it does lock
>because of the "short" feedback loop that turns intopositive feedback.

Ok, but the same feedback path ensures that there is only a very small
input differential voltage for the OTA. I've been very surprised by this,
seeing that in this configuration the input divider doesn't play a big role
(if any), and that the circuit is quite linear, more than what I had
expected. I have to mention that it was Jörgen who pointed me at this.
Overdriving results in harsher clipping, rather than the soft tanh curve
which one might expect. (Leaving reversal aside.)
The circuit in question is my MS20 filter "clone", which is actually very
sensitive to amplitude, but merely because of that nonlinear feedback loop.

>The SVF structure as used in the new Formant might not be as critical to
>locking. Not that I think phase reversal sounds nice, even if it doesn't
>lock
>up ...

Agreed. 

>Why not simply use an inverting integrator, and switch the two OTA
>inputs ??

You're right, I've overseen that. 

Bye,
 René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159