Implementing PolyAT

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Voltcontrol
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Implementing PolyAT

Post by Voltcontrol » Fri Feb 21, 2020 8:33 am

Dear all,

Where can I find good resources on implementing PolyAT in a desktop synth module? (So in-out protocols over MIDI and CV/Gate for keyboards and controllers).
Gaun Yersel!

jorg
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Re: Implementing PolyAT

Post by jorg » Fri Feb 21, 2020 11:48 am

I'm not clear on the question.

Are you looking for the MIDI spec? It's readily available on the web.

CV standards for modular synths are (I'm pretty sure) pinned topics in one of the MW forums.

Or are you looking for the types of sensors you might use in a keyboard?

Maybe some other aspect?

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Voltcontrol
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Re: Implementing PolyAT

Post by Voltcontrol » Fri Feb 21, 2020 2:20 pm

jorg wrote:
Fri Feb 21, 2020 11:48 am
I'm not clear on the question.

Are you looking for the MIDI spec? It's readily available on the web.

CV standards for modular synths are (I'm pretty sure) pinned topics in one of the MW forums.

Or are you looking for the types of sensors you might use in a keyboard?

Maybe some other aspect?
I'm looking for details you'd want to consider when implementing polyAT in a desktop synth module.
Gaun Yersel!

c0ntr4d1ct10n
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Re: Implementing PolyAT

Post by c0ntr4d1ct10n » Tue Feb 25, 2020 9:43 am

I think I get it :hmm:
Are you building a desktop synth and you want to implement poly aftertouch into it so that it can be played using any polyAT keyboard (eg. I am able to use the SQ80 to play polyAT on my Roland Juno ds88 and jd-xi) - am I correct?

I would be interested to find this out as well.

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Voltcontrol
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Re: Implementing PolyAT

Post by Voltcontrol » Tue Feb 25, 2020 9:48 am

c0ntr4d1ct10n wrote:
Tue Feb 25, 2020 9:43 am
I think I get it :hmm:
Are you building a desktop synth and you want to implement poly aftertouch into it so that it can be played using any polyAT keyboard (eg. I am able to use the SQ80 to play polyAT on my Roland Juno ds88 and jd-xi) - am I correct?

I would be interested to find this out as well.
Correct!
Gaun Yersel!

jorg
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Re: Implementing PolyAT

Post by jorg » Tue Feb 25, 2020 9:58 am

Voltcontrol wrote:
Tue Feb 25, 2020 9:48 am
c0ntr4d1ct10n wrote:
Tue Feb 25, 2020 9:43 am
I think I get it :hmm:
Are you building a desktop synth and you want to implement poly aftertouch into it so that it can be played using any polyAT keyboard (eg. I am able to use the SQ80 to play polyAT on my Roland Juno ds88 and jd-xi) - am I correct?

I would be interested to find this out as well.
Correct!
Hey Contra - excellent guesswork. Pretty amazing you got it first try, with so many different possible meanings and so little to go on.

The hard part is the keyboard; if you assume you have a PolyAT keyboard, then you just need to parse the MIDI messages and distribute AT to your synth voices as you distribute pitch and velocity. You'll want to provide a way to assign the AT information to a choice of parameters.

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Voltcontrol
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Re: Implementing PolyAT

Post by Voltcontrol » Tue Feb 25, 2020 10:03 am

I've found some info here: https://sound.stackexchange.com/questio ... aftertouch

If any of you have actual implementation experience it would be super if you can share.

Cheers!
Gaun Yersel!

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TheMentat
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Re: Implementing PolyAT

Post by TheMentat » Tue Feb 25, 2020 10:16 am

I’m in the process of updating the firmware for the Ambika to accommodate MPE (midi polyphonic expression) so this stuff is pretty fresh in my mind. If you are programming the midi parser yourself, the Ambika code might be a good place to start:

https://github.com/pichenettes/ambika

If you have any questions, fire away!

More broadly, If you are designing a synth, you may as well implement MPE as well... it allows polyphonic control of aftertouch, in addition to polyphonic pitch slides and timbre changes (typically via CC74). Several new midi controllers support it, and it is summarized here (full specification is at midi.org):

http://www.rogerlinndesign.com/mpe.html

c0ntr4d1ct10n
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Re: Implementing PolyAT

Post by c0ntr4d1ct10n » Tue Feb 25, 2020 10:50 am

I'm also wondering how difficult it would be to "hack" an existing midi synth which doesn't respond to any type of aftertouch to give it polyAT. Apparently this diy hardware is supposed to be able to provide this: https://larsee.com/blog/tag/midimixfix.html

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TheMentat
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Re: Implementing PolyAT

Post by TheMentat » Tue Feb 25, 2020 11:47 am

c0ntr4d1ct10n wrote:
Tue Feb 25, 2020 10:50 am
I'm also wondering how difficult it would be to "hack" an existing midi synth which doesn't respond to any type of aftertouch to give it polyAT. Apparently this diy hardware is supposed to be able to provide this: https://larsee.com/blog/tag/midimixfix.html
I'm not sure that tool will do what you are hoping... I got the impression that it modifies input data and outputs it via midi to the synth. If that is the case, I think the best one could do with that is to map the "channel aftertouch" to a CC message that the synth responds to, and get "mono aftertouch". If the synth's internal midi parser doesn't explicitly handle either poly aftertouch, or permit some MPE-like approach that uses one note per channel, I think you'd need to dig into the software or replace some hardware...

weasel79
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Re: Implementing PolyAT

Post by weasel79 » Thu Feb 27, 2020 11:57 pm

you can search through the github of the axoloti project, there's full MPE implementation and with that i am sure some poly AT code to be found.
https://github.com/axoloti

iirc poly AT is just one midi message (#2 ?) with note and "pressure" as data1/data2 respectively.

not much i know about your project but you might wanna look into implementing full mpe instead as that seems to become a quite usable standard with a bunch of new devices recently.

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