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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Thu Jun 21, 2012 8:08 pm Post subject:
MIDI CV Insanity? |
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When I started on this journey (and I'm not even far enough to have a full complement of VCO/VCF/VCA at the moment, so my cart is running WAY ahead of my horse) the lightbulb that got me started was MIDI->CV and a copy of the MTS-100 that I found while looking for midi + Arduino projects.
I adapted the MTS-100 by 1) using an Arduino and coding it myself and 2) omitting anything but basic MIDI in, CV/Gate/Trig out. For what I'm doing right now (i.e. nothing, but soon to be a tiny bit) that's plenty. The keyboard I started with has no pitch bend, so why would I want that?
As I go along I keep having ideas about how I should have done it. And I got a couple cheap semi-busted keyboards I believe I can recondition, and they are Rolands with the Pitch/Mod controller. All of them (including the one I started with) are also velocity sensitive, though none have aftertouch.
I sat down tonight and buzzed through a few different commercial MIDI-CVs to see whether my ideas hold water, and I found a few things that were interesting. All of them seemed to rely on hidden controls, whether it was dip switches changing the configuration of outputs, or an LCD and menu system. This seems to go against a general analog synth UI design tenet that the controls should all be right there. Additionally, while there were some pretty impressive features, they all seemed to be either/or kinds of output controls, limiting the number of outputs. So there could be 8 CV outs, with matching gates, but then that config has no triggers or other associated outputs (of course 8 outs is an awful lot ).
My idea is actually a little different... I'm thinking a two voice unit. A MIDI in and MIDI through jack. Each voice to have 6 outputs: CV, velocity, pitch bend, modulation, gate and trigger. Each voice can be following Omni mode or a specific one of the 16 MIDI channels. To set the channel, each voice will have a 1 digit display and a knob; if the knob is all the way down, the channel is Omni and the display is blank, otherwise it displays 0 - F (and of course would have knob markings to indicate 1- 16 for those not comfortable with hexadecimal )
One thing this doesn't do is allow for aftertouch or other more exotic controls. But the tradeoff is having everything out front instead of being assignable or whatever.
That is going to be one big panel 16 positions for jacks and controls, and 2 positions for the MIDI jacks. I'm using 5U and 1/4" jacks, so extra big...
I'm curious if anyone has any thoughts on whether this would really be useful, and/or why nobody is doing anything like that (real estate space?? that does seem like reasonable justification for hiding controls; PIC / DAC limitations?).
Please note--this is all pipe dream at the moment, and I have NO experience doing anything remotely like production work much less PCB layouts, so I'm NOT proposing that i go into business making such a beastie, nor am I soliciting for interest in kits or PCBs or ANYTHING. Just kicking around ideas, and by all means, if someone else wants to implement something like this, more power to you. I'd even be interested to help, assuming I were to have enough free cycles (highly unlikely any time in the foreseeable future...another reason besides raw inexperience that I'm NOT proposing a business model here). |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Thu Jun 21, 2012 10:52 pm Post subject:
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Some follow up questions based on additional research...
From what I can tell, CV typically ranges 0 - 10V, pitch -1V to +1V, and other voltages 0 - 5V.
Resolution is important for the pitch so you get a smooth transition.
But I'm finding that it looks hard to source DACs... 16 bits are very expensive, able to do +/- 15V can be expensive depending on what kind of settling time you want. Expensive being on the order of $20 per chip in small quantities. Even 12 bits aren't great from that standpoint. Looked at Mouser, DigiKey and Jameco, as well as Tayda (no luck) MCM (no luck) and Unicorn (not great luck).
for the MTS-100 I only used an 8 bit DAC but I've seen it said repeatedly that's no good for pitch bend unless you like the stepping sound.
So I'm also curious what folks think about voltage ranges, resolution, and sourcing.... |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
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Posted: Fri Jun 22, 2012 3:29 am Post subject:
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Couldn't you add a glide circuit to the 12bit version? Variable speed, smooths out the steps. Still, I s'pose it has to settle somewhere hey? A lot eaiser if you can send exact notes from the DAW. _________________ What makes a space ours, is what we put there, and what we do there. |
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diablojoy
Joined: Sep 07, 2008 Posts: 809 Location: melbourne australia
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Posted: Fri Jun 22, 2012 9:05 pm Post subject:
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try perusing the midibox forum and wiki, lots of good info on midi to cv implementations there.
$20 bucks for a 16 bit DAC is a good price
I got 6 x max525's direct from maxim but that was a long time ago
and they were a hell of a lot dearer then that. _________________ In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sat Jun 23, 2012 8:12 am Post subject:
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I will make another run at MIDIbox before I actually try something like this...I've looked at it before and been somewhat confused, but perhaps if I have a specific target that I understand in mind it will help get through it.
Thanks for the reference
I don't think I meant to say $20+ for the DAC was a bad price, just a bit out of my budget range for a single module that is likely to have multiple DACs. |
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