code: function subtract (a, b) {
    var fifths = b[0] - a[0]
    var octaves = a[1] !== null && b[1] !== null ? b[1] - a[1] : null
    return [fifths, octaves]
  }
docs: Subtract two pitches or intervals. Can be used to find the distance between pitches.
  
  @name subtract
  @function
  @param {Array} a - one pitch or interval in [pitch-array](https://github.com/danigb/pitch-array) format
  @param {Array} b - the other pitch or interval in [pitch-array](https://github.com/danigb/pitch-array) format
  @return {Array} both pitches or intervals substracted [pitch-array](https://github.com/danigb/pitch-array) format
  
  @example
  operator.subtract([4, 0, 0], [3, 0, 0]) // => [1, 0, 0]