Analog Pitch Shifter Idea

[Rene Schmitz]

At 18:31 09.03.1998 -0800, you wrote:
>Hi folks:
>
>I came up with a fledgling idea for an analog pitch shifter, using
>bucket-brigade delays.  Feel free to shoot it down if necessary - all input
>is welcome.
>
>My idea for one would be a derivative of a frequency shifter, and would use:
>
>- A quadrature function generator, that generates sawtooth and triangle
>waves that are 90 degrees out of phase.
>- Two bucket-brigade delay lines (semi-short ones, like the SAD 1024).
>- Two VCAs.
<snip>
This is a variation of a sheppard function generator, just simplified to two
channels
(a sheppard has usually 4) if you want to further improve this thing you
could go octature.
(45deg shift)

>For changing the pitch of the above circuit, I can think of two methods.
>The speed of the oscillator could be changed, as higher frequencies would
>generate more extreme pitch shifts.  The drawback would be that any glitches
>would be shifted up in frequency with higher pitch shifts, eventually
>becoming audio rate.  The other method would be to use a pair of multipliers
>to control the amount of sawtooth that goes to the BBD clocks.  With this
>method, you could go from positive to negative pitch shifting by varying the
>sign of the control voltage fed to the multipliers.  The glitches could at
>least be manifested as more of a tremolo-type sound with this method.
>
>Would this work?  Any idea how much pitch shifting could be realized with
>this circuit?  How long of a delay line would be optimal?  Would the
>Panasonic delays have wide sweep ratios necessary to get nice wide pitch
>shifts, or would the Reticon devices be needed?

Its not a matter of maximum pitchshift, but merely of the bandwidth that you
want.
Therefore the bandwidth requirements would limit the maximum shift, and
therefore a
longer delayline (i.e. more buckets/higher clock) seems useful to me.

>Once again, any and all input appreciated.  If anyone has an idea how the
>older pitch shifters worked, I'd love to hear it.

I'm not shure but this scheme could be the way, since one can also implement
it in software, where it is usually done this way.

Bye
 Rene

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