Instrument Synthesis

The Gameduino's sound system is a 64-voice synthesizer. Each voice generates a pure sine wave at a certain pitch and volume.

Using the sound processing package Loris, you can analyze a one-note instrument sample to generate a graph of how its key frequencies (or "partials") develop over time. This graph shows the 16 strongest frequencies in a single :download:`piano note <piano.wav>`, and how their volume peaks at the beginning of the note, then decays over the next second or so.

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A little more code (Loris has a Python interface, fortunately) turns this note data into a form that the Gameduino can play directly through its 64-voice synthesizer. There are several of advantages of doing this instead of using a straight sample:

The encoding is done by this Python program ( - it reads the note samples and writes Arduino data into a header file for each instrument. The format of this instrument data is:

To play back the note, the Arduino sets up the frequencies for all used voices, then updates the voice amplitudes for each time step:

  PROGMEM prog_uchar *instr = piano;
  byte voices = pgm_read_byte(instr++);
  byte duration = pgm_read_byte(instr++);
  for (byte i = 0; i < voices; i++) {
    GD.voice(i, 0, (pgm_read_word(instr) * 184L) >> 10, 0, 0);
    instr += 2;
  for (;;) {
    prog_uchar *amps = instr;
    for (byte i = 0; i < duration; i++) {
      for (byte j = 0; j < voices; j++) {
        byte v = pgm_read_word(amps++);
        GD.wr(VOICES + 4 * j + 2, v);
        GD.wr(VOICES + 4 * j + 3, v);