[sdiy] analog pitch shifter circuit?

[Theo]

Hardly a answer your waiting for me think,
but the low-fi (toy) voice transposer IC might be your best bet for a one IC
pitch shifter.
The easy way to pitch shift is to use DSP.

The analogue way would be to frequency shift.
That is; modulate with a carrier frequency and then demodulate using
different frequency.
Difference between modulation and demodulation frequency is your frequency
shift.
Cause all partials are shifted the same number of hertz the harmonic
relation is lost.
Great for chipmunk voices or a bit more extreme as a voice scrambler for
secure communication (frequency shift back and you get the original)

Maybe you can do a analogue pitch shift by dividing the audio into 16 (or
more?) frequency bands,
then frequency shift each band depending to its center frequency using the
above modulation/demodulation method.
This should keep the harmonics intune, well not really but sort off anyways.

And err.., yes not a one IC solution.
On the positive side, VC of the shift is easy just use a array of VCOs for
the demodulators ;^P

The other analogue pitch shifting method I know of uses a reel to reel tape
machine where the head is replaced by a rotating drum with 4 heads.
Depending on the direction of the rotation of the drum each heads read the
tape to slow or to fast.
When one head turns away from the tape the next head takes over, either
skipping or repeating a portion of the audio.

Have fun,
Theo



----- Original Message -----
From: <synthplayer88 at spymac.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, January 03, 2005 4:35 PM
Subject: [sdiy] analog pitch shifter circuit?


> Hi guys,
> I was wondering if anyone know how does the boss voice transformer achieve
the
> voice pitch shifting?
> I would like to build an analog pitch shifter does what the Boss voice
> transformer do but I am not sure if that is an analog circuit, since all
their
> new pedals such as the  PS3 and PS5 are all digital circuits.
>
> I came accross this chip that does pitch shifting but only has preset
shift and 8
> Khz sampling rate :(
> which seems to be kinda lo fi...
>
> http://www.holtek.com/english/docum/consumer/8950.htm
>
> Does anyone know of any monolithic IC that can do what this IC does but
with more
> flexibility? eg. allows precise pitch shift of any notes up to serveral
octaves.
>
> Oh, please do not suggest any DSP or uControllers. I would like to avoid
ANY
> programming and looking for a simplest circuit to do this if possible :)
>
> How can I apply FM into this? eg. multiply the sound source by 2, 4, 8
hz.....
> Can this be done?
>
> Thoughts?
>
>