making effects pedals

[ManFromMars]

hello there
Does anyone know how to make an analogue pitchshifter ie the effects pedal that Tom Morello (rage against the machine) uses in the solo in Killing in the Name? As in, what circuitry/parts are needed and what kind of knowledge?
Cheers
ManFromMars

[bombastique]

PAIA Electronics may have something for you...
www.paia.com (http://www.paia.com)

[ursus]

It is s a digitech whammy.
http://www.guitargeek.com/layouts/display.php3?id=124

[krelnarb]

I may be wrong, but I don't believe that there's an analog pitch shifter.

I think they've all been digital (not counting that weird swoop analog delays make when you change the delay time)

It would be cheaper to buy a wammi pedal than to build one from scratch. A lot cheaper. I love mine, their fun.

k

[This message has been edited by krelnarb (edited 05-21-2002).]

[ManFromMars]

OK thanks for the help pees :-) I could have sworn that Total Guitar said that Morello used an analogue pedal though... thx anyway thoguh

[Sengoku]

I believe that it would be possible to build an analog pitchshifter in a similar way to how an AM radio modulator works. AM is achieved by shifting the audio signal up in frequency (and then back down again on your radio, although we use a different way of getting it back down again) by multiplying the audio signal (say at frequency Fa) with a cosine wave. If you look at the frequency spectrum of a signal that has been multiplied by a cosine (say with frequency Fc), you will find that the audio signal will now be at the freq Fc + Fa, along with a second copy of the audio at Fc - Fa. The audio signal has been shifted both up and down in frequency by the frequency of the cosine wave. You should be able to filter one of the two copies with a high or low pass filter, and be left with either a shifted up or down version of the original signal.
So how do we actually DO this? Probably the easiest way would be to find an AM modulator IC that lets you supply the modulating signal as well as the audio, and get a voltage controlled oscillator as your modulating frequency input. Feed the output of the modulator into a low pass / high pass filter and hopefully it somewhat resembles pitchshifted audio! I've been toying around with that idea in my head for a while now, and while I suspect it should do a reasonable job, I can't say I've actually tried it myself yet – but theoretically it should work (might be tough making it sound nice though ;).

Pitchshifting is usually done in effects pedals digitally because its quite easy to do with a processor (stick your cosine in a lookup table and away you go), and its ultra easy with a processor to add something like delay as well, so Boss can crank out their pitchshifter/delay pedals with the delay added as a kinda afterthought :). Hope this helps any. If you don't understand any of it, I'm happy to explain it further.