GK3 MIDI Pickup out to Propeller out to MIDI

Peter1950

Hi,

I have been looking for a pitch to midi unit and they are all really expensive. I figured if I bought the GK3 MIDI Pickup and use the propeller chip to decode the audio signal coming from the polyphonic pickup to send out a midi signal it would be a lot cheaper that spending $800. I don't know where to begin. The concept is pretty easy to grasp but executing seem difficult. If someone could give me some direction or help I would really appreciate it.

Thank you

SexieWASD

I'm actually really interested in this as well, even if it is way over my head. At the least I would like to know how to get the fundamental frequency so that a propeller guitar tuner could be made, or perhaps to record tabs on the fly if it were quick enough.

Bob Lawrence (VE1RLL)

re"direction

The prop can do it no problem. The pickup you have, has 6 hex coils in it. think about each coil as being on a channel. Design one channel and get it working, then copy that circuit for the other 5 channels for a total of 6(one per string). I would use a cog per string + 1 for the serial object. A cog per string is not necessary but I believe it make coding easier and allows for more flexibility per channel should you need it.

A very basic Example

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Channel 1:

From the MIDI pickup you'll need take the output from a coil and put it through a low noise preamp. The input level (threshold) should be adjustable via a variable resistor (pot). From the pre-amp you need to go through a A to D (not delta sigma as per the prog Edu book, use a chip based one such as the Microchip line) converter to convert the audio to digital and feed it to a propeller input pin. Once it's inside you have to write software to figure out the pitch of the note. Once you have the pitch you can select a midi note from a lookup table in the software. You can then use the serial object (setup for MIDI) to transmit MIDI note on-off, note number etc and send it to an external sound module (there is one available that's prop-based)

I may add more to this later because I just thinking out-loud at this point.

You could do it all in spin as a proof of concept and later you could update a few modules to asm if required, for speed.

For the code you need:( list is not any particular order) ADC conversion finished? , Pitch detection, is detected value relevant?, threshold value, Peak values, increase velocity Averages, Freq to MINI note lookup table , note on ,note off, midi transmit, etc.

then hardware you wold have a few LED's for Power, signal input LED for each channel, TX MIDI, etc.........

Fenta7

I bought a GVOX guitar. It has the hex pick up and an amplifier for each pick-up on the bridge. The amplifiers volume can be adjusted. How do I get started in programming the propeller chip to recognize pitch detection and converting it to MIDI. For example: if pitch A is 440hz the MIDI out would have a channel number, note number and a velocity signal. This could be sent to a rack mount sound module or a virtual instrument in the computer.

Thank you