[sdiy] Frequency to MIDI Conversion

[Richard Wentk]

At 15:09 18/02/2003 -0500, R. D. Davis wrote:
>Has anyone on the list experimented with any sort of frequency to MIDI
>conversion?  Since my Juno-60 has no MIDI output, and the DCB<->MIDI
>converters aren't inexpensive, I was thinking about just converting
>the line-level output to MIDI somehow... haven't spent much time
>thinking about it, but before I attempt to figure out some circuitry
>(or software, using sound-card input) for this, I thought that I'd
>check to see if anyone else had attempted something like this.

This can't be done polyphonically from an audio signal. There are ways and 
means that work kinda sorta for certain timbres, but not reliably in any 
general sense.

You're much better off tapping into the keyscanning matrix and using that 
to create a MIDI output with the help of a simple cheap processor chip like 
a PIC. It's not quite a trivial operation, but if you can code a little 
it's not too complicated either. And you'll get an absolutely clean and 
reliable MIDI out, which an audio based system won't ever give you.

It helps that the Juno 60 (nice sound, by the way...) isn't touch 
sensitive, so all you need to do is worry about note ons and note offs. If 
you want you can add a simple slow ADC to digitise a control voltage input 
from (say) a pedal and use that to add some velocity-like variation.

Don't forget running status when coding the interface.

A more advanced project would be to add an *input* to the key scanning 
circuit and decouple it from the original keyboard out, to give you both 
MIDI in and MIDI out.

If you're worried about cutting up your synth, I'd guess all the note 
information is available at the DCB port. If you use that for note input 
and output you can create your own MIDI interface without any surgery. I 
don't know what the DCB spec is, but I'd imagine it's online somewhere. Or 
if not, someone on this list will have it.

Richard