[sdiy] Time-varying all-pass filters

Rutger Vlek rutgervlek at gmail.com
Thu Jan 6 15:13:17 CET 2022

Hi Neil,

 Yes that schematic on page 22 describes very well what I'm doing, but with
an audio rate modulation signal added to the tracking cv of the all pass
filter. The problem occurs when input signal peaks and is added to twice
the output signal of the low pass filter when IT peaks. That can happen
when receiving a sudden change in the modulation CV.


Op do 6 jan. 2022 13:08 schreef Neil Johnson <neil.johnson71 at gmail.com>:

> Hi Rutger,
> > Then it occurred to me that, assuming the input is a sine wave, a phase
> shifted version up to 180 degrees could be obtained from modulating an
> all-pass filter that is also tracking along with the pitch of the
> oscillator.
> See page 22:
> https://www.soundsemiconductor.com/downloads/ssi2130datasheet.pdf
> Implementation here:
> https://www.youtube.com/watch?v=bq-2UQ6zkSU
> That was modulated at a slow (manual) rate, so no idea what it does at
> faster rates.  Interesting question though....
> > ps. Happy healthy new year!
> Happy new year to you too!
> Cheers,
> Neil
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