I don't remember the spects but yes it could generate more then one sound at a time Music and sound effects even. Just it was rather sketchy in the latter by today's standards. Adlib really was designed to be a music card. You also must remember that digitized speech was really ground breaking stuff at the time.
Yes, on the programming side Adlib music synthesis was really nice, given the right libraries. You could start a tune playing and it would keep going, and even repeat, all on its own. This meant your program could spend all its precious CPU cycles for graphics and simulation. I've even seen games crash unrecoverably, while the music kept playing without trouble.
I never worked much with digitised sound libraries under DOS (let alone interacting with the hardware directly), so I'd welcome anyone with more knowledge. However, I'm pretty sure that the rules for the Sound Blaster 1.0, 1.5 and 2.0 were:
- You could queue up one digitised sound effect for the Sound Blaster and have it play. The duration you could queue would be determined by the amount of system memory you were willing to give up.
- The Sound Blaster could happily mix that one digitised sound with FM synthesised music without complaint.
- When CD audio became possible, the hardware also combined that with a single digital input.
- However, if you wanted to play two or more digitised sounds simultaneously, your program had to spend CPU cycles doing the mixing, ending with a single waveform for the sound card to play.
I do remember that playing module files (made popular on the Amiga and Atari, these contained multiple digitised instrument samples instead of FM synthesis) was programmatically complex, and required ongoing work by the CPU at very close intervals. Several DOS games did include such music in the early 90s, but at first they only did so during the title screen and other non-gameplay moments.
Star Control II (November 1992) is the oldest game in my own collection that plays digitised module music - and mixes it with digitised sound effects - during gameplay. However Star Control II has programmatically simple 2D graphics. While they rotate, the rotations are pre-drawn, and scaling is in multiples of two.
There probably are older games - maybe even some that predate
Wing Commander II (September 1991). However, I think it's safe to say that trying to mix multiple digitised sounds while displaying 3D graphics of WC2's complexity would have made an already bleeding-edge game unplayable. The programmers made the right decision to concentrate on digitised speech, but after a decade of configuring Sierra games, it's weird to hear a Roland do the sound effects.