begin:
FOR x=20 TO 500 STEP 25
GOSUB go
NEXT x

FOR x=500 TO 20 STEP -25
GOSUB go
NEXT x
GOTO begin

go:
SOUND x,1,255,0
SOUND 500-x+100,1,255,1
SOUND x+200,1,255,3
SOUND 500-x+300,1,255,2
RETURN