The analog ways to octave up/down rectify the signal fairly severely, so you're not quite getting out what you put in. Maybe for your application some kind of phase locked loop thing would be acceptable. It's an oscillator that tracks the frequency of an input signal.

There is no reason a capacitor sample-and-hold array would rectify the signal. Audio generally contains too many harmonics, AM, etc to have any hope of locking a PLL to it. PLL's require spectrally clean reference signals.

megathor wrote:There is no reason a capacitor sample-and-hold array would rectify the signal. Audio generally contains too many harmonics, AM, etc to have any hope of locking a PLL to it. PLL's require spectrally clean reference signals.

The octave up/down circuits on the table here are diode rings and divide down. Square wave city.

I know they typically divide or multiply with, for instance, the boss stomp boxes. As you said, though, that method would be impossible to use to shift up or down at intervals other than integer multiples.
Sampling the waveform into a capacitive array would allow you to play it back at any multiple of the sampling clock, allowing a pitch shift of any interval. The most difficult part is building a huge ass capacitor sampling array. People have done it, though, for analog delay pedals.

Here's an idea, one that I've used.
Run your guitar through a splitter into the instrument in of a ring modulator and the instrument in on an octave divider. Run the output of the octave divider into the carrier in on the ring modulator and the output of the ring modulator to the amp. This will result in an octave down and a fifth up. Blend to taste.
Ex. Playing a 440 A. Since the octave divided signal is your carrier signal, your guitar will come through with three frequencies: 440 (dry), 220 (the octave down frequency subtracted from the dry is an octave down), and 660 (the octave down frequency added is a fifth up).
This was the first thing I thought of this morning, but I hesitated on posting it since 1) it has nothing to do with building a pedal and 2) not everybody has both these pedals. It's not like they can't be gotten, though. Just make sure you use a ring modulator with modulator and carrier ins.

Good thought; this is true. I forgot the fifth is 3/2 times the root frequency. You'll get plenty of other harmonics as well, though, but thats a very interesting idea. I still wanna build the capacitor sampler, though. I've been thinking about it all day.

It's doable. The dividing is being done mathematically, and depending on the chip you have some options.

I have a Rocktave Divider that I built from a kit. You can find it (with a slightly different layout from the original) here:
http://www.generalguitargadgets.com/ind ... Itemid=148

There are some notes on how to modify the modified interval here:
http://hammer.ampage.org/files/rocktave.pdf

So with that particular chip, you could add a fifth an octave down or two octaves down. There are probably other intervals available with different chip sets.

Try one of these