53769



     in the distortion more evident. You chose which poly(s) to use by
     setting the high three bits in the AUDC registers. The 17-bit poly is
     also used in the generation of random numbers; see 53770
     ($D20A).

     The clock bits allow the user to speed up or slow down the clock
     timers, respectively, making higher or lower frequency ranges
     possible. Setting the channels to the 1.79 MHz will produce a
     much higher sound, the 64 KHz clock will be lower, and the 15
     KHz clock the lowest. The clock is also used when setting the
     frequency for the AUDF timers.

     Two bits (three and four) allow the user to combine channels one
     and two or three and four for what amounts to a nine octave range
     instead of the usual five. Here's an example from De Re Atari of
     this increased range, which uses two paddles to change the
     frequency: the right paddle makes coarse adjustments, the left
     paddle makes fine adjustments:

     10 SOUND 0,0,0,0:POKE 53768,80:REM SE
        T CLOCK AND JOIN CHANNELS 1 AND 2
     20 POKE 53761,160:POKE 53763,168:REM
        TURN OFF CHANNEL 1 AND SET 2 TO PU
        RE TONE GENERATION
     50 POKE 53760,PADDLE(0):POKE 53762,PA
        DDLE(1):GOTO 30

     High pass filters allow only frequencies higher than the clock value
     to pass through. These are mostly used for special effects. Try:

     10 SOUND 0,0,0,0:POKE 53768,4:REM HIG
        H PASS FILTER ON CHANNEL 1
     20 POKE 53761,168:POKE 53765,168:REM
        PURE TONES
     30 POKE 53760,254:POKE 53764,127
     40 GOTO 40

     See the excellent chapter on sound in De Re Atari: it is the best
     explanation of sound functions in the Atari available. See also the
     Hardware Manual for complete details.

                              ALLPOT
     (R) Eight line pot port state; reads all of the eight POTs together.
     Each bit represents a pot (paddle) of the same number. If a bit is
     set to zero, then the register value for that pot is valid (it's in use); if
     it is one, then the value is not valid. ALLPOT is used with the
     POTGO command at 53771 ($D20B).

     ----------------------------------------------------------------------
53769          D209           STIMER
     (W) Start the POKEY timers (the AUDF registers above). You