[sdiy] analog pitch shifter circuit?

[WeAreAs1 at aol.com]

In a message dated 1/3/05 10:57:25 AM, t.hogers at home.nl writes:

<< 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. >>

The same thing can be done using analog Bucket Brigade Devices (Hi, Harry).  
You need to modulate the BBD clock with a sawtooth wave.  The upward-rising 
(or downward-going for lower pitches) sawtooth wave emulates the effect of the 
rotating tape head, effectively raising the pitch of the BBD output by a 
constant amount.  Well, constant until the sawtooth gets to its peak and has to 
retrace back to the bottom again...  During that retrace period, there is going to 
be a glitch in the pitch shift.  There are a handful of different ways to 
deal with that glitch -- for instance, you could have two BBD pitch shifter 
circuits being modulated 180 degrees out of phase with each other and cross-fade 
between the two with a panner/dual VCA, with the cross-fade kind of masking the 
glitch (sort of like the aforementioned two-tape-heads idea).  There may be 
some other workarounds, but none of them will be perfect, and most solutions 
will probably not be very musically satisfying.

Also, keep in mind that pitch shifters generally have a pitch range of +/- 
one octave, and they usually sound pretty horrible when shifting as much as one 
octave.  Two octaves might be technically possible, but the sound would be 
completely distorted and very likely be unusable for anything except weird noise. 
 (and not cool weird, but the "sheesh" kind of weird)

Again, someone is trying to reinvent the wheel here.  Believe me, it would be 
cheaper, easier, more musically useful, and probably even more fun to simply 
spend $100 and get one of those BOSS Pitch Shifter or Intelligent Harmonizer 
pedals.  They work amazingly well, and have features that you'd NEVER be able 
to DIY.  It would probably even be possible to modify those pedals with a CV 
input for voltage control over the pitch shift amount -- then you'd still have a 
nice DIY element happening to satisfy that part of your soul.

Mike B.

P.S. - When I ran this email through my spell-checker, I found that I had 
mistyped the words "pitch shifter" as "pitch shiter".  I thought Harry might 
appreciate that.