INT 18 - Gravis Ultra Sound YEA_GUS.EXE - RAMP VOLUME                           
	AX = 6909h
	BL = voice number (00h-1Fh)
	BH = looping type (0 = none, 1 = forward, 2 = back and forth)
	CX = starting volume
	DX = ending volume
	DI:SI = time
Return: nothing
SeeAlso: AX=6902h,AX=690Ah