More about PoKey 16-bit mode and 'distortion guitar'

[analmux]

Maybe some people here remember the PoKey 'distortion guitar'. It starts at 2:18 of the following video:

 

 

Here is a simple atari basic test to play with the possibilities of the distortion guitar. It's very curious that, using 16-bit mode, voice 2 is silent and voice 1 not.

 

Push START for smooth left modulation of the poly9 state

Push SELECT for smooth right modulation of the poly9 state

Push START + OPTION to change note downwards

Push SELECT + OPTION to change note upwards

 

10 P=53760:Q=53279
20 POKE P+8,208:POKE P+1,132
30 R=20
40 PITCH=R*511-7
50 PH=INT(PITCH/256):PL=PITCH-PH*256
60 POKE P,PL:POKE P+2,PH
70 S=PEEK(Q):IF S=7 THEN GOTO 70
80 IF S=6 THEN POKE P+2,PH+1:GOTO 130
90 IF S=5 THEN POKE P+2,PH-1:GOTO 130
100 IF S=2 THEN R=R+1:GOTO 40
110 IF S=1 THEN R=R-1:GOTO 40
120 GOTO 60
130 FOR T=0 TO 49:NEXT T:GOTO 60

This sounds curious. Does anyone have an idea how this works?

[analmux]

Here's a small modification and an easy download:

 

 

Using BASIC or TURBOBASIC, you can type:

 

LOAD "D:DG16.BAS"

TEST2015.ATR

Edited January 26, 2015 by analmux