Waveform music (multiple notes)

Actually just any multi-track music would be great. You could do something like this:

var track1 = "...";
var track2 = "...";

function note(ch) {  
  if (ch in pitches) {
    var f = 4000*pitches[ch]/1500;
    if (!w.running)
      w.startOutput(B0, f);
    else if (!w2.running)
      w2.startOutput(B0, f);
    else if (!w3.running)
      w3.startOutput(B0, f);
    else if (!w4.running)
      w4.startOutput(B0, f);
  }
}

function step() {
  var ch1 = track1[pos];
  var ch2 = track2[pos];
  if (ch1 !== undefined) pos++; else pos=0;
  note(ch1);
  note(ch2);
}

As you might have guessed by now I'm not very musical :)