[sdiy] MIDI-CV convertor idea

[Tom Wiltshire]

> On 25 Oct 2020, at 17:47, Mike Beauchamp <list at mikebeauchamp.com> wrote:
> 
> 
>> HOWEVER…a passive mix doesn’t use a virtual ground node, so there’s the potential for bleed through from one channel to another. So I did a quick simulation of the situation to see if this was a problem, shown attached. U1 takes a 0-4V signal from the Bend DAC and turns it into a +/-83mV signal. This is then fed to both mixers. The other mix input comes from the appropriate Note DAC, also 0-4V. Each mixer is then followed by x4 make-up gain, which compensates fro the /2 loss in the mixer and adds an extra x2 to turn the Note CV range into 0-8V and the pitch bend range into the standard +/-2 semitones.
> 
> Just wanted to say that pitch bend range isn't standardized to +/- 2 semitones, although that is a lot of synthesizers' default setting. The MIDI spec says that it is variable and reconfigurable to +/- 24 semitones and optionally adjustable by cents. Some other makers of continuous pitch instruments require even larger ranges, and I think this is called for in the MPE spec as well.

Yes, I understood that it’s not standardised. I think it might have begun as a General MIDI default, and it seems to be used as a “typical” value. Obviously most MIDI synths can respond to pitch bend messages however they see fit, so it’s very flexible. A 1V/Oct analogue synth doesn’t have quite the same flexibility! It will just respond to whatever voltage you feed it, and you can’t easily change that without knocking out the whole tuning. It’s true that my current design doesn’t easily allow the addition of a “Pitch bend range” parameter. Perhaps I’ll look at that again and see what I think about it.