code: function(note) { 
        var out = 0
        if (!_.isNumber(note))
          return console.error('invalid [mtof] value ' + note)
        if (note <= -1500) out = 0
        else if (note > 1499) out = this.maxMidiNote
        // optimized version of formula : Math.pow(2, (note - 69) / 12) * 440 
        else out = 8.17579891564 * Math.exp((0.0577622650 * note))
        return out 
      }
docs: TODO: round output ?