[sdiy] MIDI CC with Pots

[Richie Burnett]

I agree with what you're saying.  Maybe it isn't a problem for CCs, 
(although it certainly is for other MIDI messages like note on.)

I know that it shouldn't be a problem if a transmitted CC is received again 
a millisecond or so later, but I had worried about glitches caused if that 
CC ever ended up taking more than a handful of milliseconds to make it's 
journey to the sequencer and back.  I guess the situation I'd like to avoid 
would be looped-through CCs arriving at the synth so late that they are 
drastically out of sync with the current control value and causing the 
filter cutoff to chatter between the current value and the one from say 20 
or 30 milliseconds ago.

That's quite a massive time delay though for a realtime system like a MIDI 
sequencer, so probably couldn't happen in practice.

My Roland TR-8 seems to have something built in to the hardware to detect 
the MIDI loop condition because it pops up the message "loop" on the LED 
display if it gets it's own CC messages looped back, but it's hard for me to 
determine if it actually takes any evasive action when it detects the 
condition...

-Richie,



-----Original Message----- 
From: gordonjcp at gjcp.net
Sent: Sunday, October 05, 2014 7:59 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] MIDI CC with Pots

On Sun, Oct 05, 2014 at 07:43:30PM +0100, Richie Burnett wrote:
> In this situation is it usual to:
>
> 1. Ignore the problem while recording (it'll be fine during playback
> anyway.)
> 2. Turn off looping-through of MIDI messages at the sequencer
> 3. Turn off "local control" at the synth so it only acts on the CC
> messages after they've been sent out to the sequencer and come back
> via the MIDI IN port?

Does it actually make a difference?  You're not creating a continuous loop, 
unless your synth somehow responds to *received* MIDI CC by transmitting 
further CC.

How would your hypothetical synth respond to receiving MIDI CC from the 
sequencer as you tweak the knob?  It would probably respond to the most 
recent message, right?  So in this case, it reads the pot, saves the current 
pot value, realises it must update the voice engine and sends a CC message. 
Milliseconds later it receives a CC message for that same controller for the 
value it's already set to, so it can either update the voice engine *again* 
with no effect or be smart enough to ignore it (although this latter option 
would probably cost more CPU cycles because you'd have to compare and 
branch).

-- 
Gordonjcp MM0YEQ

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