output = (2.0^input) This is useful for converting a pitch modulation value into a frequency
scaler. An input value of +1.0 will output 2.0 for an octave increase. An input value of -1.0
will output 0.5 for an octave decrease. This implementation uses a table lookup to optimize for
speed. It is accurate enough for tuning. It also checks to see if the current input value is the
same as the previous input value. If so then it reuses the previous computed value.