Beginnings of a Teensy polyphonic voice with USB MIDI + Host

gero
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Beginnings of a Teensy polyphonic voice with USB MIDI + Host Jun 16, 2019 22:12:45 GMT admin likes this

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Post by gero on Jun 16, 2019 22:12:45 GMT

So I just posted a long text in the introduction thread and promised to go a bit more into detail what I'm planning to build as DIY modules for the AE modular.

One of the things I'm sceptical about with modulars is how hard it seems to play chords. The amount of modules it would need to make a 4 voice synth makes me shudder; and I have no idea how to even start with voice allocation. I thought about what I believe would make the easiest way to integrate polyphonic sounds into the AE while still fitting the overall concept. I'm absolutely not a purist and have no fear of the digital so I got to this:

- single digital module with 6 oscillators each with an amp envelope.
- No filter, the output should be sent through a separate filter module.
- Interface with a MIDI controller/sequencer directly to deal with multiple notes.
- CV gate output for the point where we're going from 0 voices to 1+ voices and back to 0 voices (to control a filter envelope).
- While we're at it, CV pitch and gate output for the newest note.

I chose the Teensy 3.6 as a microcontroller and started working on it this weekend. The Teensy is an amazing platform and I cannot believe how easy all of this is and how well it works. I've put in a couple of hours on Saturday+Sunday and I already have a 6 voice poly synth playable via USB, both in host mode and with regular USB MIDI. So you can either plug in a computer or just any old USB midi controller.
This is where I was Saturday, monophonic sine playback in USB host mode:

This is where I am today, 6 voices, amp env, USB host and regular USB midi, 5 waveforms and attack+release controlled via MIDI CC: gerotakke.de/public/20190616_TeensySynth.mp3
The audio output is still from the onboard 12bit DAC. I have ordered the Teensy Audio Shield with a better 16bit DAC but honestly, I'm pretty fine with the way it sounds already.
I used Valhalla Room because LUSH PADS, other than that there's no processing.

So far so good! Super happy with it. But I gotta say, this was the part that I'm most comfortable with. I'm not great at electronics and I have zero experience with CV. There are a lot of things for me to figure out and I will probably ask some questions here once I start working on the electronics side of things.

I plan on making this all open source; if you want the code at this point already, hit me up.

If you have any suggestions, please let me know.
I'll keep you updated.

Cheers

Gero

timb0bsteve
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Posts: 34

Beginnings of a Teensy polyphonic voice with USB MIDI + Host Jun 17, 2019 18:24:02 GMT via mobile

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Post by timb0bsteve on Jun 17, 2019 18:24:02 GMT

I was looking to use the teensy as well for my AE system once it arrives. I think I am going to try and do some DSP FX with it.

I am 100% with you on digital oscillators. I don't particularly mind if they're digital or analogue, just as long as they work :-P

I'd love to see the code. Will you throw it up on GitHub?

Congrats on the work so far! I can't wait to see where you end up with this :-)

gero
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Posts: 6

Beginnings of a Teensy polyphonic voice with USB MIDI + Host Jun 23, 2019 10:41:40 GMT admin likes this

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Post by gero on Jun 23, 2019 10:41:40 GMT

Hey,
@tim0steve I've put the current code up on my domain for you. I have kind of a personal feud with Microsoft so I avoid GitHub since they've bought it ;-) Will probably end up putting it on Bitbucket.
gerotakke.de/public/201906kolibrisynth.zip

I've been thinking about this some more and did quite a lot of testing. I've decided to first got with a “minimum viable product” version because there is a lot of stuff that I have no experience with and I try to have some results before I throw myself into the deep end and then maybe never finish anything ;-)
Things like: I have never designed a PCB, I want the first version to be on a perfboard so I'll have to keep the components to a minimum.
So this is where I'm cutting corners:
No controls on the faceplate except maybe 3-4 buttons where you can save/restore presets. All synth settings will be controlled via CC. I might cook up a WebMidi interface for that.
No audio output in AEM's “DC offset style”; just route the output jack to the faceplate and then go through the master module or the 4i/o.
No CV output at all, but route all MIDI (both from Host and regular USB midi) to a traditional midi jack on the faceplate that can then go to the master module.

*Maybe* it would be a cool thing to add an audio input jack to the faceplate as well. The Teensy has the ability to be used as a class compliant USB audio device so you could potentially route AEMs output to the audio input on the module and then plug in your phone and record it without additional hardware. This is far off MVP territory but the input jack is something that would be pretty easy hardware wise and open up a lot of possibilities.

Cheers
Gero