[sdiy] analog pitch shifter circuit?

[Richard Wentk]

At 18:54 03/01/2005, Theo wrote:
>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.

You could use BBDs. ;-)

Traditional pitch shift uses a collection of delay lines. The difference 
between the write rate and the read rate defines the degree of shift. 
Because there isn't a 1:1 correspondence, you can't just circle through the 
line indefinitely as normal - you either run out of delay if you're 
shifting up or have too much left over if you're shifting down. So the 
usual solution is to switch between the two lines at a regular interval. 
While one catches up, the other plays out, and vice versa.

This inevitably makes the effect rather gargly and rough. You can minimise 
this firstly by cross-fading rather than switching, and secondly by using 
more delay lines and overlapping them. The more you use the smoother the 
output gets.  Effectively it's a form of real-time granular resynthesis. 
It's probably easier to implement using a DSP than any other way, but 
there's no reason why someone couldn't build a version out of memory and 
discrete logic.

Or, as I said, a couple of BBDs would work too. But not nearly as well. :-)

Richard