Problem sending Cc messages to external synths

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Problem sending Cc messages to external synths

Post by Los. » Mon Sep 07, 2020 7:57 pm

Apologies if this has already been discussed somewhere, I am new to all this and I'm not sure of the correct terminology which makes it rather hard both to search and to explain my problem!

When I send CC messages to control the filter cutoff of my external synths (microkorg, bass station 2) the changes I hear aren't sudden or 'snappy' - that may have left you scratching your head so let me give you an example.

If I draw an envelope in a midi clip that should emulate how an LFO square wave would affect the filter cutoff the result I hear is somewhere between a square wave and a triangle wave - I see vertical lines in my envelope but I hear slopey lines. (Stop me if I'm getting to technical!)

I have tried with multiple audio interfaces, synths, and in the case of my bass station I have tried sending midi via USB as well. It might be worth mentioning that I don't have any latency issues when I send midi notes.

Do I need a more powerful laptop for better performance? I'm on Macbook pro 2015 8gb memory.


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Re: Problem sending Cc messages to external synths

Post by gross9978 » Mon Sep 07, 2020 8:56 pm

Just a thought but does the patch your using have any modulation going on on the synth itself? Like an lfo or envelope controlling the filter? If so you’d be modulating it again with the midi ccs. I’ve totally done this before haha.

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Re: Problem sending Cc messages to external synths

Post by TLW » Tue Sep 08, 2020 8:17 pm

I can think of a couple of things that might be going on.

MIDI is a serial protocol - only one MIDI command can be sent or received by e.g. a hardware synth at a time. If your envelope consists of just two points - say 0 and 127, giving you a vertical line, then only two MIDI commands get sent. If there are more points between 0 and 127 each of those values gets sent one after the other, each value requiring a certain amount of time to be sent and a certain amount of time for the synth to react to them. The result can sound “smeared”. Poly synths can suffer a similar problem with chords slightly smearing because each MIDI note in the chord gets sent one at a time rather than all the notes being sent at once. This can even occur using the synth’s own keyboard or knobs if they work by sending a MIDI command to the MIDI control chip in the synth itself - which is how many MIDI equipped but otherwise analogue synths work. Voltage control usually avoids this issue altogether.

Another problem might be how handling CC changes has been implemented in the synth itself. Some react almost instantly, though all synths take a little time, usually a very few milliseconds, to interpret and apply MIDI commands. Others apply something a bit like portamento either deliberately or as a by-product of their digital control hardware and software, to smooth the changes out a bit. That can be a good thing as it avoids some changes which if applied fully instantly would lead to things like popping noises, and it can be a limitation as well.

All of the above, if happening, should only take a few milliseconds. If what you are hearing sounds more like a slow filter sweep then, as gross9978 says, there may be something else going on. Modulation applied to the filter or the filter envelope settings fighting the CC change so you are trying to send the filter frequency one way while the envelope or an LFO is trying to send it the other way are certainly possibilities worth checking.
Live 10 Suite, 2020 27" iMac, 3.6 GHz i9, MacOS Catalina, RME UFX, assorted synths, guitars and stuff.

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