Changing the pitch

[ment4lbre4kdown]

Having played around with alot of circuit bending on toys and stuff, I just had a thought. Shouldn't it be really easy to build a pitch shift pedal? Anyone got any ideas?

[nick d]

                       Possible - yes .  Easy - not really . Search Rocktave , E&MM Harmony Generator , to name but two .
                        Or buy a Digitech Whammy .

[brett]

Hi
Balanced and ring modulators do this.  Aliasers do something similar.  the search function is your friend.
Octaves modulate the signal with itself.
cheers

[Taylor]

No.

Pitch shifting is among the hardest effects to do. The reason it's easy with circuit bent stuff is that you are working with either a synthesized note, where changing voltage or resistance equals pitch change, or a pre-recorded note where you just have to speed it up or slow it down to get pitch change.

Working with a real-time audio signal is many orders of magnitude more complex. Some ways to do it:

Spin semiconductor FV1 - this is an integrated digital chip which already has pitch shift programs written for it. You just need to code your selected shift amount or range.

"Exploded" digital shifter - this is an idea I'm working on. Take a quadrature oscillator, turn it into sawtooth waves and use these to modulate delay time of 2 PT2399 delay chips. Use triangles derived from the original quadrature oscillator to crossfade between the outputs of the 2 delay chips. Use an OTA to control amplitude of sawtooth waves - this is your shift amount control, which can be a treadle ala the Whammy.

HT8950 - this chip is very ugly, lo-fi, and limited in shift amounts, but easy. Google "hazelwanter pitch shifter".

[~arph]

I tried modulating a pt2399 with a sawtooth once. The problem was with the sawtooth itself. If the falling edge isn't instantaneous the whole pitch shifting doesn't work. I guess by crossfading between two pt2399's you can avoid the falling edge. Is that what you intend with the crossfading?
Sounds like a tricky circuit, but doable.

[Mark Hammer]

Taylor's absolutely correct.

If you want to consider full-wave rectification, or frequency-dividers as "pitch-shifting", then I suppose that is a qualified 'yes'.  But the sort of continuous pitch-shifting that one might do with keyboards that generate an electronic signal via digital or analog oscillators IS bloody hard to do.

As always, I refer people to the review of the old A/DA analog harmonizer in Device, circa 1979.  That'll give you an idea of how"easy" it is to do in analog form: http://hammer.ampage.org/files/Device1-4.PDF