Polyphonic Synth

synth.cpp

#include <Audio.h>
#include <MIDI.h>

typedef struct {
  AudioSynthWaveformSine osc;
  byte note;
  float freq;
  float amp;
  AudioConnection w_lft;
  AudioConnection w_rgt;
} Voice;

AudioOutputAnalog      uselessOutput;
AudioOutputUSB         audioRet;
AudioMixer4            mixA, mixB, mixC;
Voice*                 voices;
unsigned char          activeVoices, i;

void setup() {
  AudioMemory(32);

  activeVoices = 0x00;

  voices = (Voice*)malloc(6 * sizeof(Voice));

  // Connect the first 3 voices to mixA
  AudioConnection v0mA(voices[0].osc, 0, mixA, 0);
  AudioConnection v1mA(voices[1].osc, 0, mixA, 1);
  AudioConnection v2mA(voices[2].osc, 0, mixA, 2);
  
  // Connect the last 3 voices to mixB
  AudioConnection v3mB(voices[3].osc, 0, mixB, 0);
  AudioConnection v4mB(voices[4].osc, 0, mixB, 1);
  AudioConnection v5mB(voices[5].osc, 0, mixB, 2);
  
  // Connect mix A and B to mix C
  AudioConnection mAmC(mixA, 0, mixC, 0);
  AudioConnection mBmC(mixB, 0, mixC, 1);
  
  // Connect mix C to Output L and R
  AudioConnection mCoL(mixC, 0, audioRet, 0);
  AudioConnection mCoR(mixC, 0, audioRet, 1);
  
  // Serial will be used for debugging messages.
  Serial.begin(9600);

  // Callbacks for note handling.
  usbMIDI.setHandleNoteOff(OnNoteOff);
  usbMIDI.setHandleNoteOn(OnNoteOn);
  
  Serial.println("Teensynth (teensy-unth) v0 @ " __FILE__);
}


void loop() {
  // Continuously read and handle MIDI messages.
  usbMIDI.read();
}

void OnNoteOn(byte channel, byte note, byte vel) {
  for(i = 0; i < 6; i++) {
    // Serial.printf("i = %d \t v = %01x \t a = %01x\n", i, (1<<i), (activeVoices & (1<<i)));
    if ( (activeVoices & (1<<i)) == 0) {
      //Serial.printf("Voice %0d on.\n", i);
      activeVoices |= (1<<i);
      voices[i].amp = 1;
      voices[i].note = note;
      voices[i].freq = noteToFreq(note);
      voices[i].osc.amplitude(1);
      voices[i].osc.frequency(voices[i].freq);     
      break;
    }
  }
  Serial.printf("Active Voices: %0x\n", activeVoices);
}

void OnNoteOff(byte channel, byte note, byte vel) {
  for(i = 0; i < 6; i++) {

    //Serial.printf("i = %0d \t v = %02x \t a = %02x\n", i, (1<<i), (activeVoices & (1<<i)));
    //Serial.printf("v[i].note = %02x\n", voices[i].note);
    
    if(voices[i].note == note && (activeVoices & (1<<i)) != 0 ) {
      //Serial.printf("Voice %0d Off.", i);
      
      voices[i].note = 0xff;
      voices[i].amp = 0;
      voices[i].osc.amplitude(0);
      activeVoices &= ~(1<<i);

      break;
    }

  }

  Serial.printf("Active Voices: %0x\n", activeVoices);
}

// Convert MIDI note to tonal freq.
//
// Formula: 440 * 2^( midi_note_val - 69) / 12)
float noteToFreq(byte note) {
  float freq = 440 * pow(2, (float(note - 69) / 12));

  // Serial.printf("Note: %x // Freq: %.2fHz\n", note, freq);
  
  return freq;
}