Commodore Amiga Hardware Reference Manual page 171

Notes for table 5-7:
In this scale, the frequency for the note A is
440.0
Hz and A# is the twelfth root of
2 (1.059463)
times higher in frequency than A. The note B is the twelfth root of
2
higher than A#. This is followed by 0, 0#, D, D#, E, F, F#, G, and G#, and
goes back to A at 880.0 Hz, an octave higher, and so on. Use this scale for
waveforms where the fundamental is 2 to the nth bytes long and where n is an
integer. For example, for A at 440.0 Hz with a period of 508, the sample table con-
tains 16 samples per cycle:
3579545
clocks/second
=
16 samples/cycle
508 clocks/sample X 440 cycles/second
n=4
It follows that for A at
440.0
Hz with a period of
254,
the sample table has to con-
tain
32
samples per cycle (AUDxLEN
=
16).
The general rule is that doubling the sampling frequency (halving the sampling
period) changes the octave of the note being played. Thus, if you playa 0 at a
sampling period of 256, then playing the same note with a sampling period of 128
gives a 0 an octave higher.
Before using the lower octaves in this table, be sure to read the section called "Alias-
ing Distortion." .
Audio Hardware
159