OC-2 fundamental extractor

[anotherjim]

OC-2 looks like an adaptive comparator - no fixed reference, average versus peaks I think. E-H guitar synth has an adaptive Schmitt trigger.

Zero crossing detection at simplest is a comparator with one input fixed at the Vref of the audio. You can make them reject false triggers when the signal is down to  noise by adding hysteresis (positive feedback), but if you have peak detection too it shouldn't be necessary.

My idea, as I recall, and I doubt that it's an original one, was to say - first get a positive peak (and set), wait for zero crossing, then get a negative peak (and reset), wait for zero crossing then so on...
Seemed foolproof at the time, but we have an instrument that can produce harmonics stronger than the fundamental. I'm told that the human brain has the ability to sense the fundamental when the harmonics are much stronger - it knows 880Hz and 1320Hz is a pitch of 440Hz without hearing the 440Hz! Tough job to make circuits that can do that.

[merlinb]

So instead of just filtering the those Frequencies to ground it throws them at the output 180* out of Phase for more effect?

A simply RC filter has a fairly gentle roll-off. Too gentle for some applications. Sometimes you want no loss at all up to the cut-off frequency, then sudden and very rapid attenuation. A Sallen and Key filter uses an RC filter, but it also applies a little positive feedback around what used to be the gentle roll-off region. This sharpens it up, exactly as you observed.

[thehallofshields]

Merlin, your U-Boat is a work of art. Care to shed some light on your Comparator section?

[merlinb]

Merlin, your U-Boat is a work of art. Care to shed some light on your Comparator section?

A similar question came up recently, try here:
http://www.diystompboxes.com/smfforum/index.php?topic=76997.msg1014425#msg1014425

[espectro]

hello, someone can load again the schematics of the fundamental extractor, thanks

[merlinb]

hello, someone can load again the schematics of the fundamental extractor, thanks

It's the lower half of the chopped OC-2:
http://www.diystompboxes.com/smfforum/index.php?topic=76997.msg732767#msg732767

[espectro]

hello, someone can load again the schematics of the fundamental extractor, thanks

It's the lower half of the chopped OC-2:
http://www.diystompboxes.com/smfforum/index.php?topic=76997.msg732767#msg732767

thank you my friend