polysynth

synth.cpp

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


// Each concurrent note is assigned to a voice.
// The voice tracks which note is being played so
// when it is relased the correct voice can be stopped.
typedef struct {
  // A pointer to the oscillator so it can be controlled.
  AudioSynthWaveformSine* osc;

  // MIDI Note
  byte note;

  // Note Frequency
  float freq;

  // Note amplitude.
  float amp;
} Voice;

// The actual oscillators for the voices
AudioSynthWaveformSine voice0, voice1, voice2, voice3, voice4, voice5;

// A non-USB output is required for the audio engine to run.
AudioOutputAnalog      uselessOutput;

// Return audio over USB
AudioOutputUSB         audioRet;

// 3 Mixes are used so downmix the 6 voices to a dual-mono output.
AudioMixer4            mixA, mixB, mixC;

Voice*                 voices;

// activeVoices is a bitmask of the currently playing voices.
unsigned char          activeVoices, i;

// Connect the first 3 voices to mixA
AudioConnection v0mA(voice0, 0, mixA, 0);
AudioConnection v1mA(voice1, 0, mixA, 1);
AudioConnection v2mA(voice2, 0, mixA, 2);
  
// Connect the last 3 voices to mixB
AudioConnection v3mB(voice3, 0, mixB, 0);
AudioConnection v4mB(voice4, 0, mixB, 1);
AudioConnection v5mB(voice5, 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);

void setup() {
  AudioMemory(32);

  activeVoices = 0x00;

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

  // 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__);

  //AudioSynthWaveformSine* v0 = &voice0;
  

  //Serial.printf("v0 = %0x\n", voices[0].osc);
  // Doesn't like this for some reason... not sure why :(
//  voices[0].osc = &voice0;
//  voices[1].osc = &voice1;
//  voices[2].osc = &voice2;
//  voices[3].osc = &voice3;e
//  voices[4].osc = &voice4;
//  voices[5].osc = &voice5;

  pinMode(13, OUTPUT);
}


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

  // Turn the LED on if any notes are playing
  digitalWrite(13, activeVoices);
}

void OnNoteOn(byte channel, byte note, byte vel) {
  // If all 6 voices are playing just return.
  if (activeVoices == 0x3f) return;
  
  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);
/*
      AudioSynthWaveformSine* osc = voices[i]->osc;
      
      osc->amplitude(1);
      osc->frequency(voices[i]->freq);     
  */    
      break;
    }
  }

  showActiveNotes();
  
  //Serial.printf("Active Voices:\t\t %02x\n", activeVoices);
  //Serial.printf("Audio Memory:\t\t %02x\n", AudioMemoryUsage());
}

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;
/*
      AudioSynthWaveformSine* osc;
      osc->amplitude(0);
  */    
      activeVoices &= ~(1<<i);

      break;
    }

  }

  showActiveNotes();
  //Serial.printf("Active Voices:\t\t %02x\n", activeVoices);
}

// Debugging function which shows the currently playing notes.
void showActiveNotes() {
  Serial.printf("[%10lu] Notes:\t\t", millis());
  
    for(i = 0; i < 6; i++) {
      if ( (activeVoices & (1<<i)) != 0 ) {
        Serial.printf("%02x ", voices[i].note);
      } else {
        Serial.print("-- ");
      }
    };
   
  Serial.print("\n");
}

// Convert MIDI note to tonal freq.
//
// TODO: Replace this function with a lookup table of frequencies
//       mapping the midi notes to frequencies.
//
// 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;
}