Tuner is a software chromatic tuner for determining the musical pitch of a
sound as well as how close that pitch is to the established value for the note.
Tuner listens on the NeXT's CODEC microphone input and computes a frequency for
the sound it samples. It maps this frequency onto a musical note and displays
the value. Then it looks up the standard value for the note to display the
difference between the standard value and the computed frequency.
The tuner can compute pitch using two different algorithms, by counting zero
transitions and by doing a fast Fourier transformation (FFT) using the DSP
array routines. You need a relatively simple waveform for the zero transitions
algorithm to work -- some instruments and voices work better than others. When
it works, it has a potential accuracy of about +/- 1/4 Hz. The FFT algorithm
is able to handle more complex waveforms but currently only has a potential
accuracy of about +/- 2 Hz. (The zero transitions algorithm works well with
recorders and the FFT algorithm works better with bassoons.) The potential
range of both algorithms is C00 to B7 and both are further constrained by the
limits of the microphone.
lane@sumex-aim.stanford.edu