code: function toFreq (p, tuning) {
    if (NUM.test(p)) return +p
    var midi = toMidi(asPitch.parse(p))
    if (!midi) return null
    tuning = tuning || 440
    return Math.pow(2, (midi - 69) / 12) * tuning
  }
docs: Get the pitch frequency in hertzs
  
  @param {String} pitch - the pitch
  @param {Integer} tuning - optional tuning, 440 by default
  @return {Float} - the pitch frequency
  
  @example
  pitch.toFreq('A4') // => 440
  pitch.toFreq('A3', 444) // => 222