[sdiy] Polyphonic MIDI to CV

Brian Willoughby brianw at audiobanshee.com
Fri Jul 9 21:04:10 CEST 2021


You could add a VCA between the LFO and the oscillator(s) so that the CPU can change the depth without getting into stepped quantization. You could tie LFO depth to the MIDI Modulation controller value (either 7-bit or 14-bit or whatever your DAC can support).

If you design separate PCB for the digital (CPU) and analog circuits, then you can stack the analog sections for a different kind of ensemble effect. Each analog board could share all of the control signals except LFO, and then you'd have a magnificent detuning effect. You could mimic some string synth designs by having each analog board LFO at the same frequency, but out of phase with each other. You could also just have each analog board LFO at a different frequency since adding an LFO is cheap and that might sound more natural. With the CPU generating LFO, you could easily implement both as options.

Reverb would certainly be useful, but that could be shared among all voices since it's a LTI process (well, most reverb algorithms are LTI).

Brian


On Jul 9, 2021, at 11:07, francesco mulassano <francesco.mulassano at gmail.com> wrote:
> Interesting point, I just need to have note on and note off messages, the rest is all manual, there are no presets. I'll add an lfo on the pitch to have a detune effect and a reverb before the release
> 
> Il ven 9 lug 2021, 18:37 Brian Willoughby <brianw at audiobanshee.com> ha scritto:
>> What sorts of circuits are voltage-controlled in your project? i.e. What do the various CV signals control?
>> 
>> It's certainly possible to build a MIDI to CV circuit that handles more than the typical standalone MIDI-to-CV. As one example, the old Prophet VS has 60 CV channels inside. Do you know how many CV you'll need?
>> 
>> You don't really need CV to turn on each voice, but a simple analog switch. The problem with a switch, though, is that it does not impart velocity. If you want velocity in a top/divide then you'll need 128 VCA circuits to cover the full MIDI range of notes. If you don't have 128 VCA, then your full polyphony will be reduced to the number of VCA that you have.
>> 
>> Brian
>> 
>> On Jul 9, 2021, at 07:45, francesco mulassano via Synth-diy <synth-diy at synth-diy.org> wrote:
>> > Logan has top generator with dividers and BBD for the 'fx'
>> > 
>> > Il giorno ven 9 lug 2021 alle ore 16:44 Oren Leavitt via Synth-diy <synth-diy at synth-diy.org> ha scritto:
>> >> What type of tone generation does this project use? Top octave generator/dividers were typical in many 70s string synths.
>> >> 
>> >> - Oren
>> >> 
>> >> On 7/9/21 9:09 AM, francesco mulassano via Synth-diy wrote:
>> >>> as a feature, however, I would really like to use the original scheme as much as possible and remain analog as possible (apart from midi, lfo and reverb)
>> >>> 



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