Atari XL

Sound and Music
91
100 DATA 81,2,81,2,88,1,81,1,72,
2,96,4,108,4,122,2,122,2,128,1
,122,1,108,2,144,8
The next program uses DATA statements to playa
tune in four part harmony. There are five D AT A
items for each group of notes - the periods of the
four voices, and a value for the note length. The
program will play a tune you should recognise if
you have run the Audio-Visual self checking
routine on the XL.
It will take you quite a time to type in all the
DATA, but the end result is well worth all the
effort.
You will notice that the values used for note
periods are not the same as those given in the Atari
BASIC Reference Manual supplied with your XL.
We found that the values given by Atari were not
well tuned, and that the note values given in
Appendix 11 sounded much better! Even so, the
tuning is not perfect, as the 255 available periods
are not sufficient to give a perfect sound. Later in
the chapter we will describe how to increase the
range and tuneability of the XL at the expense of
reducing the number of voices from four to two.
10 D=10
20
VQ=0:Vl=1:V2=2:V3=3
30 VOL=4:VOLO=lO:VOL3=6
100 READ PO,Pl,P2,P3,T
110 IF T=255 THEN END
120 SOUND VO,PO,D,VOLO
130 SOUND Vl,Pl,D,VOL
140 SOUND V2,P2,D,VOL
150 SOUND V3,P3,D,VOL3
155 FOR DEL=O TO T*llO:NEXT DEL
160 GOTO 10