new Formant book arrived

[René Schmitz]

At 00:24 07.11.00 +0100, jh. wrote:

>That refers to MS-20 type filters and Polygon filters now ? (just to
>be sure). 

Yes, but rather to the local feedback OTA+cap+buffer arrangements. 

>For low frequencies, yes. Feedback loop linearizes the
>OTA's input stage. But for higher frequencies, loop gain decreases
>and nonlinearities become valid again. 
>In LPF polygon filters, the
>amplitudes for later stages are lower at these critical frequencies,
>because it's filtered by previous stages, so you won't notice much
>unpleasant artefacts. The one case where you *really* have to fight
>nonlinearities is the all pass filter - there the soft clipping sounds
>nasty IMO.

Yes, its like opamp distortion, at least for the LPF. Feedback systems
always have rising THD with rising frequency. Thinking about it, wouldn't
it make sense to increase the loop-gain? E.g. by getting rid of the OTAs
input attenuators, or at least use less attenuation. (What are they good
for here, anyway?)

In the case of the allpass/notch, artefacts will clutter up your notches
again. I would want any distortion to occur before the notches. Or am I
missing other uses for allpasses here? 

Bye,
 René

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