Pitch Shifter Project

[JesusAstronaurt]

So I just got an idea to make a guitar effects pedal that shifts pitch down to simulate Alternate tunings. It'd be best as a standard effects box configuration, running on a 9V power supply and input and output jacks. I've been trying to think of how to make a circuit that would do this and run into several questions:

1) Is it possible I can go about Modulating the pitch while keeping the general timbre and quality of the sound to stay roughly the same? Obviously some tone coloration will have to occur, but can I keep that at a minimum?

2) I'd like to be able to set the pedal to several different tunings. I could make 5 different pedals for 5 different tunings, but that's completely impractical. I'm thinking having either:

a) a potentiometer to have manual control over the pitch. The problem with that is where and how should I wire that in order for it to effect the level of frequency modulation. (Obviously I need to have an idea of what the circuit's going to be before this question is applicable, but does anyone have ideas?)

-or-

b) having a switch that can easily change the pitch by half steps. The problem with this is how can I calibrate each setting to be exactly a half step each time, when musical pitch is logarithmic rather than linear. I'm thinking having some freakin' intense and EXACTING capacitor and/or resistor usage in there, but the math behind getting them to be exactly right seems waaaaaay too intense for me. I might be wrong on that though, it could be easy as hell, I dunno. Is this a good route to take at all?

3) Does anyone know of some other device/ effects pedal designed for this purpose I could take some hints from or rip off entirely?

Any help is greatly appreciated!

 

[Blueteeth]

For analogue:
There are various octave effects, that will add an octave up or down 'on top' of your guitar signal (lots of usage in the late 60's, 70's). You may be able to remove your original signal entirely by cancelling it out...subtracting it....from the output signal.

For shifting the pitch up or down in discrete steps, ie: semi-tones, you're looking at a digital approach, which, is not for the faint hearted....and waay beyond the beginner electronics engineer, or even intermediate. However,since guitar signals are not as bandwidth hungry as hi-def audio, you may be able to get away with 12-bit at 32Khz sampling. For lo-fi effects, some high speed 8 bit microcontrollers can do pitch shifting using external RAM, but it really isn't easy by any means. For anything remotely close to commercial effects from boss, or like the digitech whammy the cost of time taken to build such a device becomes much more than the price of buying them. (I know, theres no fun in just buying something )

Note: using a guitar effects pedal, no matter how expensive, to shift your guitar signal up or down a few steps will sound different from actually tuning your guitar by the same pitch. Different tunings means the strings are different tensions, and so, produce difference levels of harmonics. Thats why a D string fretted at the 5th fret sounds different to an open G. - even though they are the same pitch.

Also, the guitar effect will only shift the whole guitar up or down, the intervals between the strings remains the same, so you're restricted to down tuning to D, C or even B for metal, or up for some country styles. Open D/G/E tunings will string require the old fashioned approach.

So, just to reiterate, your best bet for a DIY pedal would be some octave effects. Look here:

I'll give it a think, there may be a way of controlling an oscillator to run at a frequency related to the input frequency, like using a PLL (phase locked loop), but it would by no means sounds like a 'guitar'.

Blueteeth