MIDI to CV, Pitchbend and More


Today I did some further experiments on the next little improvement to the MTG Turbo CPU for the Sequential Circuits Pro One: MIDI-to-CV. I’ve acquired a quad DAC (D/A or digital-to-analog converter) board that can be very easily hooked up to the CPU module in order to control a few more parameters in the Pro One.

For now I’ve tested controlling three parameters of the Pro One:

  • Pitch (Osc 1 and/or Osc 2)
  • Filter cutoff freq
  • Filter resonance
  • VCA ADSR/volume (I haven’t played around with this yet).

Therefore, taking input from MIDI or from within the CPU itself, here are some possible sources of data to control those parameters:

  • MIDI Pitch Bend, Mod Wheel, Aftertouch, Velocity
  • Other MIDI continuous controller(s)
  • The internal sequencer data
  • A soft-LFO that features a variety of waveforms including sample and hold (S&H)
  • MIDI Clock/Sync??

For now I’m thinking it would cost about $25 to add these features to and existing MIDI+CPU setup. And it would be very easy to install. Now coming up with a nice clean way for the end user to control it all — that will be a challenge.

Any other ideas or comments?

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11 Responses to MIDI to CV, Pitchbend and More

  1. grantb4 says:

    Well I don’t think the “VCA ADSR/volume” thing is going to work out.

    On the bright side, Osc and Filter control is VERY easy — solder a wire and that’s pretty much it. The current firmware has some noticeable “zippering” if you move the MIDI pot controlling the filter, but theoretically I can use interpolation to smooth that out.

    I already tested the S&H -> Filter cutoff and the effect is very sweet. Synching that to MIDI clock will be an awesome feature (though perhaps a little cliche).

  2. grantb4 says:

    The pitch bend is done! I added support for Pitch Bend Range adjustment (AKA Pitch Bend Sensitivity) via either SysEx or RPN 0,0.

  3. Carlos says:

    Hi,
    How about being able to control Portamento /Glide? Being able to switch it on/off and to control the time would be awsome. The Kenton midi/cv converter I use currently supports this feature…Your doing great work. Is it finished?

    • grantb4 says:

      Hi,
      No, it’s not finished. 😉 There is still some work to do on the CV stuff and other refinements. Also the CPU supports USB so it is theoretically possible to hook it to a PC without a MIDI interface, but that’s just a twinkle in my eye at the moment.

      Regarding the Portamento/Glide question. Unlike external CV units, the Turbo CPU uses the existing internal DAC, so in that case it has no control over portamento. However, the optional CV board has a DAC of it’s own so it might be possible to experiment in this direction.

  4. slalum says:

    Hi,
    I have a keyboard-less Pro-One and I was wondering if, by hooking it up with the Turbo processor and MIDI option, I would be able to use the Pro-One’s “Glide” via MIDI. The CV input on the synth actually by-passes the glide circuitry which I would like to be able to use since my MIDI-to-CV converter doesn’t have this feature built-in.
    Thanks,
    slalum

  5. slalum says:

    Good to know, thanks.

  6. Jeff says:

    Hey there,
    I’m very interested in buying the “Turbo CPU + MIDI + CV” but I don’t see it on ebay.

    Please advise.

    Jeff

    ps- I really believe in keeping these rare gems alive and kicking and I think this update is a dream come true.

  7. Jeff says:

    So, I just bought this update, but realized that I may need to write you offline to talk about the CV beta. Please contact me!

    best regards,

    Jeff

  8. grantb4 says:

    I have lots of DAC chips. Contact me at the email address at the bottom of the MTG website home page.

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