Octave Box With Individual Octave Waveshaping? - Synth Like

[facon]

Hey,

I'm looking for a way to manipulate the individual octave signals in an octaver. I'm attempting to put together something like a Micro Synth with many more options. My first step is to approach the octave section. I would like to utilize a circuit that is already out there and add additional sections to achieve the end result. I've been looking at the Madbean Low Rider pcb as a starting point. I was hoping to tap into each octave before the individual volume pots.

Octave Down -1 & -2
It looks like most octave down circuits use something similar to the MXR Blue Box. Since the signal is crushed into a square wave before flip-flop, I would assume the best way to manipulate the waveform is to find a circuit that will take a square wave and allow me to manipulate it to triangle, sine, sawtooth, ramp, etc? Something like a lag processor to help me achieve sounds similar to the other synth waveforms. Since I'm dealing with a signal that is not consistent like a synth, I don't know if this is possible. It doesn't have to be perfect, I'm just looking for synth-like and am not expecting to make it sound exactly like a synth.

Direct Guitar
I want to add a circuit to shape the direct signal. Since this is usually just a clean blend of the guitar, it needs to be converted into something that sounds synthy/fuzzy. It will need to have similar characteristics as the low octave so the over all sound feels cohesive. Perhaps I could use the same Schmidt trigger or square wave fuzz that is used into the octave down?

Octave Up
There seem to be a few ways floating around for an octave up. I can't find any that convert the signal to a square wave similar to the lower octave. This may be a good thing since it might be quite harsh, but I would still like to figure out how to manipulate it similar to the previous two. Any suggestions?

Forgive me if there is something like this already out there. It's very hard to search for all of the different random circuits that are available. I'm not skilled enough to design circuits just yet, but I can read schematics and can figure out how to add different circuits into certain points.

[R.G.]

See http://www.diystompboxes.com/smfforum/index.php?topic=105622.0 for an approach to octaves up and down done with square waves and PLLs.

Combining PLLs for frequency multiplication with additive harmonic synthesis and Johnson counter sine generators with electronic organ techniques can be a huge help.

There is a real problem in generating the variants of triangle (ramp and saw) from squares in that you have to know the frequency to adjust the slope so that the amplitude remains constant. You can do this, but the analog design gets tricky and error prone.

[facon]

R.G., you're my hero. Thanks! I'll be keeping my eye out to see if there are any developments/changes with that circuit. Time to start researching and experimenting.

[R.G.]

Well, there's more work to be done to make this pan out. My life keeps getting in the way of me doing fun stuff. I was a bit disappointed in the harshness of the sound from the first builder's work, but I suspect some tinkering would help.

I think that the 16x or 32x output from the multiplier could be run into a shift register sine generator and produce a nice following-sine.

Hmmm. Actually *any* of the outputs could be run into a shift register generator and produce a nice(ish) sine at a lower frequency too.

[facon]

Is there anything that I can do to help? I don't understand circuit design very well, but I can experiment with component values as long as I have some direction. I was thinking about etching a pcb or bread boarding the circuit. If I went the PCB route, I can socket whatever components still need tweaking and could swap around or use pots until I find the right values.

As far as the waveform manipulation part, I could add switching jacks before each of the R7 pots so I could add effects individually like an effects loop to each octave. This would allow me to start manipulating the waveforms in various ways until I achieve the desired results. Since I also want to add an attack decay and gate for each octave, it makes sense for me to go this route.

BTW, it's really hard to read the schematic on the thread. It's too small and the font makes it hard to see what's going on.