OPL3 and General MIDI

serqetry · Post by **serqetry** » 2023-09-17, 21:30:08

Hi,

I've been trying to figure out how DOS/Soundblaster games select instruments for music. I have read that it's General MIDI that the old soundcards used to play a bank of FM instruments. I discovered the DAFM synth BLASTER YMF262, and on their site it seems to imply this: "Includes the 128 General Midi 4-OP instruments designed by The Fat Man and used in 90's PCs videogames".

Now there are also devices like Retrowave OPL3 Express and the OPL3LPT which aren't actually full synthesizers, so I'm not sure where these tiny devices get their instrument data for this General MIDI that games supposedly use. These devices seem to be plug and play, and sound just like an old Soundblaster ISA card when you play a DOS game with them.

Does anyone understand how this works?

Post by **ValleyBell** » 2023-09-17, 22:58:24

The mapping from "General MIDI" to "FM instrument setting" is done by the sound driver, which is a piece of software that reads music data and translates it to commands that e.g. an OPL sound chip understands.
In case of DOS games, it is just a small DOS program like "Miles Sound System" (XMI sound driver) or SBFMDRV (Creative's CMF sound driver).

OPL3LPT only replaces the FM synthesis part, i.e. the OPL sound chip itself. So what you replace happens later in the chain than the GM -> FM instrument mapping.

serqetry · Post by **serqetry** » 2023-09-17, 23:24:53

ValleyBell wrote:The mapping from "General MIDI" to "FM instrument setting" is done by the sound driver, which is a piece of software that reads music data and translates it to commands that e.g. an OPL sound chip understands.
In case of DOS games, it is just a small DOS program like "Miles Sound System" (XMI sound driver) or SBFMDRV (Creative's CMF sound driver).

OPL3LPT only replaces the FM synthesis part, i.e. the OPL sound chip itself. So what you replace happens later in the chain than the GM -> FM instrument mapping.

Ahhh ok, that makes sense. I had assumed cards like the Soundblaster had the OPL instrument data for GM sounds stored in ROM or something, I hadn't considered it might be in the driver.

Thanks!