[sdiy] Polyphonic MIDI to CV

Benjamin Tremblay btremblay at me.com
Sun Jul 11 05:37:42 CEST 2021


@Adam, I enjoyed the article.

> On Jul 10, 2021, at 10:18 PM, Adam Inglis (synthDIY) <synthdiy at adambaby.com> wrote:
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>> On 11 Jul 2021, at 11:29 am, Brian Willoughby <brianw at audiobanshee.com <mailto:brianw at audiobanshee.com>> wrote:
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>> On Jul 9, 2021, at 13:59, Tom Wiltshire <tom at electricdruid.net <mailto:tom at electricdruid.net>> wrote:
>>> On 9 Jul 2021, at 18:49, Rutger Vlek via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>>>> Interesting project! I have been playing with the same idea for a while. It's quite a challenge to replace keyboards with buss bars typically used in divide down architectures. The range probably does not need to cover alle 128 midi notes, but at least the range of a stringer. A large array of quad VCAs (2164) could do the trick, but is rather costly. Via mcu you would be able to combine VCAs for multiple octaves on a single key (something normally done with multiple buss bars).
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>>> I think we need to be looking at the electronic organ tech this string machines were derived from. There’s a ton of stuff there about how to do polyphonic enveloping/gating of signals for cheap. Mostly along the lines of the Roland swing-type VCA with transistors, CMOS switches, or logic gates.
>> 
>> I recall that the TR-808 uses these transistor VCA circuits. Are they called "swing-type" because the output has a DC offset? I think the CV for the VCA level ends up appearing as a DC offset, but that's reasonably solved by AC-coupling the output to the next stage of the audio mixer. I also recall that the TR-808 has simple Decay envelopes.
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> <Bridged T osc.png>
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> I grabbed this from my blog post about Roland drum voices from this era.
> I think it originally comes from the CR8000 SM, but the 808 is similar
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> cheers
> A
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> https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html <https://mezzoauto.blogspot.com/2017/06/roland-cr-8000-compurhythm.html>
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