The audio subsystem of Active Worlds 3.1 has been upgraded to use DirectSound, which is part of DirectX from Microsoft.

One benefit that DirectSound brings to Active Worlds is the ability to play more than one sound simultaneously. Thus, background sounds created with the sound command no longer need to be interrupted in order to play sound effects triggered with the noise command; instead, in Active Worlds 3.1 noises now play on top of any background sounds.

Another benefit is that DirectSound provides support for MP3 files.