code: function (settings) {
    var tempo = 60e6 / settings.tempo; // Microseconds per beat
    var setTempo = Buffer.concat([new Buffer([0, 0xFF, 0x51, 0x03]), padNumber(tempo, 3)]);
    var length = setTempo.length + trackFooter.length;
  
    return Buffer.concat([trackHeader, padNumber(length, 4), setTempo, trackFooter]);
  }
docs: Return a buffer with a MIDI track that sets the tempo