filter waveform question

[Toni Jovanovski]

At 10:04 17-08-98 -0700, Christopher MacDonald wrote:
>Hi,
>
>I have built a diode ladder filter and have a question about the output
>waveforms I am getting.  I have posted some oscilloscope photos at:
>
>http://www.evenfall.com/diy/dladder.html
>
>I am wondering if anyone might know what is causing a "jump" or
>discontinuity near the peak of the waveform when the resonance control
>is turned up.  I have spent hours tinkering with the circuit and can't
>figure out what is wrong.  Sigh.
>
>
>Thanks,
>
>-Chris MacDonald
>

Hmm, I think that there isn't nothing wrong.The ' problem ' is the
resonance of the filter , who makes ' jumps ' in the peaks of signal.This
can be prove very simple using mathematics , like Fourier or Laplace
transform.Sometimes you must use math ( I hate to say ) , especially in
Filter design.There is a lot of analogue filters , like Butterworth ,
Chebyshev I & II ... But in a synth design with simple waveforms ( saw ,
pulse , triangle ) it's a question of luxury.BTW , it's not very easy to
make them voltage controlled...

I think , in synth-design , that fourth-order VCF ( four poles in same
place ) is fairly enough.

Toni Jovanoski