code: function (format, numTracks) {
    var chunklen = padNumber(6, 4); // MIDI header is always 6 bytes long
    var ntracks = padNumber(numTracks, 2);
    var tickdiv = padNumber(ticksPerBeat, 2);
    format = padNumber(format, 2); // Usually format 1 MIDI file (multuple overlayed tracks)
  
    return Buffer.concat([midiHeader, chunklen, format, ntracks, tickdiv]);
  }
docs: Given a number of tracks, return a MIDI header