Hi @rolfdegen. Thanks for sharing.
Overall this project looks good and sounds cool! The Teensy v4 is clearly a capable MCU with it's fast ARM Cortex-M7.
I'd be curious to hear about what motivated you to get started with this project and to build off of the Electrotechnique TSynth v4 foundation (http://electrotechnique.cc/)?
You also chose to use a minimal control surface, so I'm guessing you're envisioning more of a sequenced, MIDI CC message type of interaction, rather than a live, interactive performance?
Cheers