Sound in D2X-XL used to be simple stereo: a sound was louder or quieter and came more from the left or more from the right, and that was all it could tell you.

Sound effects are now played with OpenAL, which places them in the space around you, including above and below; you can hear where a robot is before you see it.

Sound also travels through the mine the way you would have to fly: how loud it is depends on the way from its source to you, not on the straight line through solid rock. A sound from the room next door reaches you from the door or opening it comes through, and closed doors and walls only let a little of it pass, quieter and duller than it was.

Rooms now have reverberation, and D2X-XL works it out by itself for every level, so level authors don't have to do anything for it: large caves ring for a long time, while narrow tunnels stay dry. Under water and in lava everything sounds muffled, and so it does in fog.

The strength of the reverberation can be set in the effect options. In expert mode there is also a dialog with detailed settings for those who like to tinker with it: