Control hacked korg monotron from Audio Codec shield DC

Control hacked korg monotron from Audio Codec shield DC

Postby instantplaces » Sun Nov 11, 2012 5:48 pm

I have a hacked Korg Monotron that accepts DC voltages 0-5 for pitch and gate-- schematic is attached. Using Max/Msp pitch tracking through a MOTU Ultralite (DC coupled) I can get guitar notes to trigger pitches on the synth. It would be great to do a version of this with Audio Codec shield and Arduino or Maple or some other microcontroller. If this is in the realm of possibility any pointers/suggestions would be appreciated!
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Re: Control hacked korg monotron from Audio Codec shield DC

Postby guest » Sun Nov 11, 2012 8:52 pm

it should be possible, but the real question will be "how well does it work?"

we just finished an FFT/FHT library for the arduino, and this could give the dominant frequency. the update rate is around 200hz, and it gives 256 bins. if you ran the codecshield at 22khz sampling rate (11khz frequency spectrum), this is 128 real bins from 0hz to 11khz, or 85hz resolution. that really isnt enough to find a note in the low registers.

you could probably get away with running the codecshield at 8khz, since the guitar doesnt produce a fundamental above 4khz. and lets say you wanted 5hz resolution, thats 800 real bins, or 1600 samples. that is too much memory for the arduino, but a maple can handle it. so it comes down to finding an FFT library for the arm cortex m3, which im sure somebody has written (although i have no references off hand). any c library should work for it. you will need to scale up to 2k samples. so it just depends upon how fast that particular FFT library is. im guessing it wouldnt be worse than a 50ms update rate, which might be a bit slow.

the final thing required would be a little buffer amp that converts the 3.3v out of the codec to 5v levels.
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