[sdiy] SVF High Pass Mode not Cutting Off

[Neil Johnson]

rob wrote:
> Thanks for the help, I tried lower integrator cap values (220pF instead
> of 470pF) but without any change. I have plenty of Freq range. on the
> pot. A sawtooth waveform is "squashed" to a flat line as Freq is turned
> up but a very sharp spike is left at the trailing edge of the saw no
> matter what the VCO freq is. Any thoughts?

Isn't that supposed to happen?  You're seeing all the high frequency 
harmonics in that sudden change, and the filter is removing all the 
lower ones hence the 'flattening'.

Try sweeping a sine wave with the filter cutoff frequency set to some 
fixed value.  You should see (if you plot the amplitude) the shape of 
your filter.

Or feed it some white noise and look at the spectrum.

Cheers,
Neil
-- 
www.njohnson.co.uk