STM32F407VG Discovery Midi Synth

Extension of the https://github.com/rogerallen/stm32disc_synth1 project adding USB MIDI keyboard input and synth configuration over serial bus (USART2 on PA2 & PA3) connected to computer.

I did this for learning purposes. Feedback is welcome.

Goals

• Next step in making a synth.
• use STM32CubeIDE
• USB MIDI Keyboard Control
• using HAL & BSP_AUDIO Stm32 Firmware
• a basic, "reasonable"-sounding synth
• polyphonic, wavetable-based synth
• resonant lowpass filter
• reverb
• user button to reset & reprogram synth

To Do

• Add USB Hub so I can have both keyboard midi device and control midi device connected. Having USB-connected PC control would be great, too.
• fix the FIXMEs

Usage

• git clone this repo
• add repo to STM32CubeIDE
• compile & run
• plug in midi keyboard (via USB OTG adapter cable) to send note on, note off messages
• listen to sounds
• connect computer to serial bus to USART2 on PA2 & PA3
• press user button to reset & reprogram synth

Note

If you run in Debug mode, the full 10-voice synth will fail because it cannot keep up.
Change the number of voices to 2 in synth.c.

Coded for clarity, not necessarily performance.

Reprogram Synth

press user button, the orange LED will activate & this will cause it to output

begin edit mode
{
  wave      = 0
  voices    = 10
  attack    = 200
  decay     = 200
  sustain   = 800
  release   = 200
  scale     = 300
  cutoff    = 600
  resonance = 5
  wet       = 750
  delay     = 1500
}
Enter 'variable value' (e.g. 'attack 500').
End edit mode with '.' 

wave, voices, cutoff and resonance are unscaled but the rest of the values are scaled by 1000. (scanf %f was giving me grief so 1.0 is now 1000)

!!! Be careful. Read the code for setting ranges. No error checking. !!!

Enter in settings and finish with a .

wave 1
attack 800
cutoff 1000
.

License

Who the heck knows? I pulled stuff from everywhere to make this. It is likely GPLv2 due to usbh_MIDI.

usbh_MIDI by Xavier Halgand (GPLv2) via https://github.com/MrBlueXav/Dekrispator_v2 biquad by Sean Connelly (MIT) via https://github.com/velipso/sndfilter reverb written by me but inspired by https://github.com/YetAnotherElectronicsChannel/STM32_DSP_Reverb