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Clean octave up/down schematic


Mixolydian42

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After playing around with a Micro POG for a bit, I'm thinking of designing a guitar organ pedal. Essentially all I would need would be a filter (to get the guitar signal as close to a sine wave as possible), a compressor (to add sustain), and several pitch shifters. A Leslie sim would be nice too, but that's probably way out of my league.

 

Anyways, basically what I'm wondering is how a clean octave up works (I understand how and why a rectifier works, except I'm looking for something that's relatively clean). How about an octave down?

 

Also, I'd ideally like to have a full 9 drawbars, which would mean having non-octave harmonics (for example, octave + 5th) as well. Is it possible to do this without going digital?

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Doesn't the Blue Box do 2 octaves down? I guess it would probably be pretty easy to change it to 1 octave down (or, if I have to, just pair it with an octave up). But I doubt it uses a clean octave down in the first place, since there's no point in going out of your way to make it clean when there's just going to be a crapload of fuzz applied to it anyways (and I wouldn't be surprised if the fuzz is created by their method of octaving down in the first place).

 

Also, I realized something that might make this project a lot harder... is a clean octave up going to be polyphonic? If the answer is "not necessarily" then does anyone have a schematic for one that is? If not, well, then I guess I might as well give up now.

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Most "analog" octave down boxes use a modified flip-flop circuit. More modern devices such as a PS3 or POG do the shifting with digital signal processing.

 

The basic idea is the input is filtered and used as a clock source for a toggling flip flop. This creates a square output with 1/2 the frequency of the input.

 

To clean up the signal, the envelope from the original signal is re-applied to the flip flop output.

 

If you want 2 octaves downs, you use a divide by 4 flip flop circuit instead of divide by two. You can also get very close to a 1.5 octave down by using a divide by 3 circuit.

 

The only think I know of that did this is the Korg PME Octave V module. It gave 2 down, 1.5 down, 1 down, normal and 1 up with additional sliders for distortion.

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After playing around with a Micro POG for a bit, I'm thinking of designing a guitar organ pedal. Essentially all I would need would be a filter (to get the guitar signal as close to a sine wave as possible), a compressor (to add sustain), and several pitch shifters. A Leslie sim would be nice too, but that's probably way out of my league.


Anyways, basically what I'm wondering is how a clean octave up works (I understand how and why a rectifier works, except I'm looking for something that's relatively clean). How about an octave down?


Also, I'd ideally like to have a full 9 drawbars, which would mean having non-octave harmonics (for example, octave + 5th) as well. Is it possible to do this without going digital?

 

 

It isn't just a filter. Think about it.

 

To go down you divide, to go up you multiply.

 

I would do the pitch detection in digital and then drive a number of sine wave oscillators for a true organ generator.

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