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I started implementing a small audio library for Arduino. It uses the PWM to generate different kinds of waves:

square
sinus
saw
white noise

The sinus wave sounds quite bad, but the rest is pretty good, especially the saw wav.

Here is the code with a small example: void audioInit(); void playWhiteNoise(int amp, unsigned long t, int pin); void playSine(int amp, int freq, unsigned long t, int pin); void playSaw(boolean up, int amp, int freq, unsigned long t, int pin); void playSquare(int amp, int freq, unsigned long t, int pin);




    define AUDIO_OUTPUT 9


void setup() { 
  audioInit();  
  randomSeed(analogRead(9));
 }

void loop() { 
  Serial.println("SAW up");
  playSaw(true, 127, currentFrequency, 1000, AUDIO_OUTPUT);
  delay(1000);
  Serial.println("SAW down");
  playSaw(false, 127, currentFrequency, 1000, AUDIO_OUTPUT);
  delay(1000);
  Serial.println("SINE");
  playSine(127, currentFrequency, 1000, AUDIO_OUTPUT);
  delay(1000);
  Serial.println("SQUARE");
  playSquare(127, currentFrequency, 1000, AUDIO_OUTPUT);
  delay(1000);
 }

void audioInit() { 
  // Make sure the PWM is at its maximum frequency.
  TCCR1A = 1;
  TCCR1B = 9;
 }


    define WAVE_RESOLUTION 32


void playWhiteNoise(int amp, unsigned long t, int pin) { 
  unsigned long startTime = millis();
  while (startTime + t >= millis()) {
    analogWrite(pin, (int)random(255));
  }
 }

unsigned char valueTable[WAVE_RESOLUTION]; void playSine(int amp, int freq, unsigned long t, int pin) { 
  amp = constrain(amp, 0, 127);
  // reuse t -> convert to number of cycles
  t = ((long)freq * (long)t) / 1000;
  // reuse freq -> convert to period 
  freq = (1000000 / freq) - 7;        // subtract 7 us to make up for digitalWrite overhead - determined empirically
  int i;
  for (i=0; i<WAVE_RESOLUTION; i++) {
    valueTable[i] = (unsigned char) ( ( (sin((2 * PI * i) / (float) (WAVE_RESOLUTION-1))) + 1.0) * amp );
  }
  while (t--) {
    for (i=0; i<WAVE_RESOLUTION; i++) {
      analogWrite(pin, (int)valueTable[i]);
      delayMicroseconds(freq / WAVE_RESOLUTION);
    }
  }
 }

void playSaw(boolean up, int amp, int freq, unsigned long t, int pin) { 
  amp = constrain(amp, 0, 127);
  // reuse t -> convert to number of cycles
  t = ((long)freq * (long)t) / 1000;
  // reuse freq -> convert to period 
  freq = (1000000 / freq) - 7;        // subtract 7 us to make up for digitalWrite overhead - determined empirically
  int i;
  for (i=0; i<WAVE_RESOLUTION; i++) {
    valueTable[i] = (unsigned char) ( (up ? i : WAVE_RESOLUTION - i - 1) * 2 * amp / (WAVE_RESOLUTION-1));
 //    Serial.println((int)valueTable[i]);   }
  while (t--) {
    for (i=0; i<WAVE_RESOLUTION; i++) {
      analogWrite(pin, (int)valueTable[i]);
      delayMicroseconds(freq / WAVE_RESOLUTION);
    }
  }
 }

void playSquare(int amp, int freq, unsigned long t, int pin) {
  amp = constrain(amp, 0, 127);
  // reuse t -> convert to number of cycles
  t = ((long)freq * (long)t) / 1000;
  // reuse freq -> convert to period 
  freq = (500000 / freq) - 7;        // subtract 7 us to make up for digitalWrite overhead - determined empirically

  while (t--) { 
    analogWrite(pin, 127 + amp);  
    delayMicroseconds(freq);
    analogWrite(pin, 127 - amp);
    delayMicroseconds(freq - 1);     // - 1 to make up for fractional microsecond in digitaWrite overhead
  }
 }

Accrochages

Audio wave functions

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