APPENDIX SIX
Sound And Music
Sound on the Atari can be quite sophisticated or quite simple,
depending on your needs and programming abilities. Simple sounds
may be input using the SOUND command; you enter the voice (zero to
three), the pitch (zero to 255), the distortion (even numbers from zero
to fourteen) and the volume (one to fifteen) in this manner:

SOUND 0,121,10,8

This will give you a pure tone middle C, moderate volume.
The SOUND command is only one way to adjust your music or sound in
the Atari. You can also POKE directly into the POKEY registers to
effect changes. For example, you can increase the normal five octave
range to nine by setting the proper bits in location 53768. This method
reduces the number of voices to two or three, but does give you quite a
range. You can use all sorts of tricks with filters, clock channels, and
poly counters, as described in the POKEY locations. For the best
description of sound control technique, see De Re Atari.
Here are the pitch values for the major notes when used with a pure
tone in the sound command:

Note         Octave 1    2     3    4     5
      C            14   29    60   121*  243
      B            15   31    64   128   255
A# or Bb           16   33    68   136
      A            17   35    72   144
G# or Ab           18   37    76   153
      G            19   40    81   162
F# or Gb           21   42    85   173
      F            22   45    91   182
      E            23   47    96   193
D# or Eb           24   50   102   204
      D            26   53   108   217
C# or Db           27   57   114   230

You can see that the intervals between notes increase as the pitch
decreases (the larger the number, the lower the pitch). Middle C is
marked with "*". Here's a simple routine to test pitch and distortion
with one voice:

5    PRINT CHR$(125): POKE 752,2
10   A = 0: B = O: C = 0
20   SOUND 0,A,B,C: POSITION 0,0
30   PRINT "PITCH", "DISTORTION", "VO
   LUME"
35   POSITION 0,2: PRINT A, B;"  ",,
   C;"  "
40   IF STICK(0) = 14 THEN A = A + 1:
    IF A > 255 THEN A = 0: GOTO 20
50   IF STICK(0) = 13 THEN A = A - 1:
    IF A < 0 THEN A = 255: GOTO 20
60   IF STICK(0) = 7 THEN B = B + 2:
   IF B > 14 THEN B = 0: GOTO 20
70   IF STICK(0) = 11 THEN B = B - 2:
    IF B < 0 THEN B = 14: GOTO 20
80   IF STRIG(0) = 0 THEN C = C + 1:
   IF C > 15 THEN C = 0: GOTO 20
90   GOTO 20

DOWNLOAD PITCH.BAS

You move the stick up or down to change pitch, right or left to change
the distortion level. Press the trigger to change the volume level. See
Softside, #30 for a similar program using all four voices and Santa
Cruz's Tricky Tutorial #6 (sound). You should also examine Atari's
Music Composer cartridge; it is not only a fine program, but it also has
excellent documentation on music, sound, and composition. There are
two excellent programs from APX, Sound Editor and Insomnia, both of
which allow you to create sounds to include in your programs (not
tunes however). Insomnia is particularly interesting in that it creates
sound which is played during the VBLANK intervals.