[sdiy] MIDI Velocity on analog synths

[Tom Wiltshire]

On 6 Feb 2014, at 03:05, rsdio at sounds.wa.com wrote:

> I agree that it would be rather difficult to make the Pro-One ADSR respond to CV directly.

The CEM3310 has CV inputs for the A,D, and R times, so those might be a good bet, but the Pro-One circuit doesn't offer a simple way to patch into them. A touch of Velocity CV to Attack time would sharpen things up. The 0 to -5V range of the times suggests to me CEM intended you could/should have an external mixer mixing the various CVs - Attack pot and modulations. So adding a mixer is doable, but becomes a serious hardware modification - not exactly plug-and-play.
What the CEM3310 doesn't have that the CEM3312 added is the Level CV to avoid a separate VCA for amount control. On the Pro-One this isn't a problem, since it's not a programmable synth and the filter envelope simply goes via a "Filter Envelope Amount" potentiometer. As Florian says, that would be the ideal destination for a Velocity CV.

> You could implement a parallel digital ADSR in the processor, and sum its output on the VCA CV input, but that might require alterations of the ADSR settings when the user makes a patch. Also, I'm not sure whether digital ADSR would perform very well with a small 8-bit.

Oh, it can be done ;) It works better than one might think. Still, his uP is probably getting pretty busy.

> In any event, glad to see you're still working on this thing!

Absolutely! Projects like this are giving a new lease of life to some venerable instruments, and making some that were never that desirable into things that people might really want (like the Prophet 600, for example). It's good work.

T.