docs: function Note( str ) {
    var couple = str.split( space );
    // frequency, in Hz
    this.frequency = Note.getFrequency( couple[ 0 ] ) || 0;
    // duration, as a ratio of 1 beat (quarter note = 1, half note = 0.5, etc.)
    this.duration = Note.getDuration( couple[ 1 ] ) || 0;
  }