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
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