[sdiy] Time-varying all-pass filters

ulfur hansson ulfurh at gmail.com
Thu Jan 6 22:58:09 CET 2022


hey rutger!

i have had amazing results with openmusiclabs sinecore design. I've changed
it a lot for my own personal needs, but the basic circuit is all there and
presented in a very informative way :) recommend checking it out!!

very best,
-úlfur

fim., 6. jan. 2022 kl. 14:16 skrifaði Rutger Vlek via Synth-diy <
synth-diy at synth-diy.org>:

> 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.
>
> Rutger
>
> 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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