[sdiy] MIDI velocity

[rsdio at audiobanshee.com]

On Apr 6, 2016, at 4:20 PM, Hugh Blemings <hugh at blemings.org> wrote:
> OnSo I did a bit of poking at a KX-76 a little while back and wrote about it here http://hugh.blemings.id.au/2015/09/26/keyboard-tinkering/
> 
> It uses the main MCU for scanning, about 1kHz update rate and appeared to adopt the stop scanning until key closure detected approach discussed elsewhere in the thread.

I've been thinking about this every since it was discussed, and I don't see how it would work for a polyphonic keyboard scanner.

One the one hand, if all you need is monophonic operation, then there's no drawback to stopping the scanning as soon as any key starts. That would simply be first-note priority. You wouldn't be able to implement last-note priority, though.

The problem with stopping the scanning is this: How do you know that another key won't trip its first switch contact while you have the scanning stopped to measure the timing from the earlier key press?

Having looked at the JU-1, where the whole key matrix is scanned on each 4 ms timer event, I can see how it might appear that the scanning is stopping and starting, but I'd like to see more details from any synth design where someone believes that velocity sensing is actually implemented by stopping the scan every time a new note is detected.

Thanks for the writeup. Fairly interesting. If you have any more timing measurements in your notes, it might be worth a followup with more details.

Brian Willoughby
Sound Consulting