I have a Hercules Soundcard Fortissimo III 7.1, digifire edition.

When I try to set the sound in Battlefield 1942 in hardware acceleration, the sound becomes terrible. (low, thud sound)

Anyone know the problem. The sound seems fine in other games.

Not all games support 5.1 surround sound, check to see if your games support these. (battlefield does) Check for the dolby sign on your games. Your sound card may have a very small hardware buffer, which will explain horrible sound and accelleration. Also check to see if your sound card is encoding in 5.1 in its hardware acceleration mode. (most software for sound cards have this option) It may be encoding 5.1 into 7.1 sound. Those are all possibilities, there are more, but not that I can think of at the time.

How can I check this?

You may be the first who finally has an possible answer. Could it be that my card is encoding in 7.1 and Battlefield does not recognize this?
But the Digifire card support 2; 2.1: 4.1; 5.1 and 7.1. I can see that in the software sound manager and equalizer.
On the other hand I don't know much about these things.