[sdiy] more pitch shifter thoughts

[PRCamann at aol.com]

In a message dated 1/3/2005 11:04:29 PM Eastern Standard Time, 
rtellason at blazenet.net writes:

> I got to thinking about this subject some time back,  and came up with some 
> 
> thoughts about things that may or may not work,  I never did get around to 
> playing with this idea.  Maybe you all could tell me why it wouldn't 
> work?  :-)
> 
> Suppose you took a PLL circuit,  one input to the phase comparator would be 
> some filtered version of your input signal.  (The filtering would be one of 
> the tricky parts,  I guess.)  The PLL is also running a top-octave chip,  
> and 
> maybe (maybe not?) some divider stages,  depending.  Things get set up so 
> that the lowest "note" available comes out at the same pitch as the filtered 
> 
> version of the input signal...
> 
> Then you've got the rest of the outputs,  the other "notes",  and maybe 
> octave-related versions of it,  all of which are going to be square waves of 
> 
> course (unless you get one of those oddball top octave setups that produces 
> an assymetric output waveform for higher harmonic content),   but in any 
> case 
> more filtering is going to be needed here...
> 
> Take a selection of those outputs and you've got "chords".  Mix them,  do 
> whatever...
> 
> Does this sound like it'd be possible to make it work at all?  If not,  why 
> not?
> 
> 
It'll work.  I built a few variations on this idea in the late '70's.  My 
favorite was a unit I dubbed the "Uglifier" -- it had a distortion section 
consisting of a Craig Anderton Ring Modulator (from the first edition of EPFM) and a 
Craig Anderton Octave Doubling Fuzz with a pot mixing the two signals; a 
tracking section consisting of a 4046 PLL with a 4024 7-stage divider in the 
feedback loop, with the divide-by-32 output going back to the comparator input of 
the PLL, and mixing pots giving combinations of 1 and 2 octaves up and 1 and 2 
octaves down; and a second tracking section using a 4046 and a 50240 top 
octave divider in the feedback loop, with a switch selecting the top or bottom C as 
the comparator input (for an octave of notes below or above the input tone, 
respectively) and two rotary switches selecting which two of the twelve tones 
would join the mess at the output.  Played a trumpet through this thing --- 
horribly lovely.   Still have it around someplace; have to fire it up sometime.

Tried using an old PMOS organ chip in the feedback loop too.  Overheated 
quite a bit at the time but it worked.  If I ever dig out the chip I'll try again.

Had an idea a few years ago for a stompbox version of it similar to the 
Anderton Roctave Divider, but never got around to building it.

But, yeah, it'll work.  The input conditioning is the hardest part....


Paul Camann
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