[sdiy] MIDI CC with Pots

Paul Burns (Fitvideo) paul at fitvideo.co.uk
Sat Oct 4 08:12:14 CEST 2014

Hi Jacob, you can see how Tom has implemented his boards here. It may throw
up some ideas. 




-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jacob Watters
Sent: 04 October 2014 06:36
To: synthdiy diy
Subject: [sdiy] MIDI CC with Pots

I had a discussion with a friend about a synth that he is working on.
We disagreed about the proper way to handle MIDI CC. Normally, I would tell
him to do it the way the works best for him, but he intends on selling the
synth. Since that is the case, then I think that it needs to work in a way
that musicians expect it to work and that it should not place unnecessary
limits on its usage. Please let me know your thought on how to handle the
following two situations.

-= PROBLEM 1: MIDI CC and Pots =-

The synth has several pots for adjusting various controls of the sound (knob
per function). The controls will also respond to MIDI CC. There can be a
conflict in how the synth responds to both messages.

OPTION 1: I recommended having the synth use whatever message it last
received, whether a pot change or a CC message. This provides flexibility in
usage and allows the use of both MIDI CC and the pots at the same time. This
is how most of my synths seem to work.

OPTION 2: The flaw with the previous method is that if a CC message turns a
value all the way down, then when the pot is moved the value will jump up to
where the pot is positioned. Encoders or a "catch up"
or "pass through" method will add a bunch of extra code that will slow
everything down and limit the abilities of the synth. To him, the sudden
change from the MIDI CC value to the pot value is not acceptable (even
though I have synths that work this way). He wants to put a switch on the
synth to change from either MIDI CC or pots. The synth will never be able to
respond to both at the same time. This limits it in that you can't adjust a
pot by hand while a MIDI sequencer changes other values automatically.

What option would you prefer? What other suggestions do you have that
haven't been mentioned?

-= PROBLEM 2: Mod Wheel =-

First, he had a control that could only be changed by the mod wheel.
The synth has no built-in mod wheel (MIDI control only) so I explained how
some synths have a joystick style pitch/mod control. On these synths, the
mod level is always reset to 0, so it would not be a good idea to use it as
a dedicate control. He agreed to add a dedicated pot to the synth for that
control. However, there is still some disagreement about how the MIDI
modulation messages should be handled.

OPTION 1: I pointed out that the mod wheel is usually used for modulating an
existing control that has its own value already. It adds more LFO to the
oscillators or opens the filter more than the current cutoff setting. It is
not usually a dedicated control on its own. This means that it only adds to
the current value of a control that is set with a pot on the synth. Since he
agreed to add an extra pot for the thing that the mod wheel will control,
this is very easy to employ and won't slow the synth down much (just add the
mod CC to the current pot value and limit it to the max value of the
control). This also means the pot for the control will have its own
dedicated CC for setting the base level, and the mod CC will only add to

OPTION 2: He wants to add a switch to change the way that the synth handles
the mod CC. This will allow the control to be disabled for anyone who is
using a joystick style pitch/mod controller. This limits the usage of the
synth for some people (anyone using it with a joystick).

OPTION 3: He also talked about the possibility of not using the modulation
CC at all. I own many synths, and all of them that have MIDI respond to the
mod wheel CC. I think that this would be a bad idea because musicians expect
the mod wheel to do something.

Again - what option would you prefer? What other suggestions do you have
that haven't been mentioned?

Thanks for your help resolving this debate!
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