This chip is used in such games as Konami's CV3j and Madara. This chip generates its audio via a 6 bit R2R ladder. This affects some registers.
Volume is linear.
G - Gate bit. In digi operation, registers 9001h and 9002h are totally disabled. Only bits 0-3 of 9000h are used. Whatever binary word is present here is passed on as a 4 bit digitized output. This chip is pretty cool.