[sdiy] Time-varying all-pass filters

[Neil Johnson]

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