carlostex wrote:There are 2 main OPL2 cards. One is the Sound Blaster Pro CT1330 and the other the original Pro Audio Spectrum. AFAIK the PAS predates the Sound Blaster Pro. So Creative, being the lamest asshole company they were, pushed a different way on how the OPL2 chips are accessed. I'm not sure if this is totally correct but on the Pro Audio Spectrum the OPL2 chips are accessed starting on address 388h and on. Sound Blaster Pro however can be accessed for AdLib compatibility on 1 OPL2 chip only via 388h and in order to use the 2 you must use the 2x0h region, standard SB ports.
SB Pro and PAS, both are Adlib compatible with ports 388h/389h, they just do it a bit differently.
On SB Pro, write to 388h/389h area writes simultaneously to left and right FM chips, so you get mono out.
On PAS, write to 388h/389h area writes only to one chip, but its output is connected to both left and right speakers via mixer setting.
For SB Pro dual OPL2 access, 2x0h/2x1h is the left chip and 2x2h/2x3h is the right chip, directly accessible.
For PAS dual OPL2 access, you'd need to write mixer to connect only left FM chip to left speaker and right FM chip to right speaker, and then 388h/389h is the left FM chip and 38Ah/38Bh are the right FM chip.
So, they are are completely Adlib compatible. If you want dual OPL2 stereo FM, your sound driver better know which card you have so it can use the four contiguous SB addresses or four contiguous PAS addresses, there's no difference in that. Except the PAS needs special mixer init first and SB just works. And since their DAC portion is different, games would need a card specific PCM audio driver anyway so they might as well have the card specific FM driver as well.