Software-mixed sound: 3D sounds are only stereo panned, but not fully spatialized (i.e. phase shifted and bandpass filtered based on sound absorption in the ear as a function of position). The sound system is limited to a maximum of 64 channels of music and sound. By default, 16 sound effects channels are allocated, leaving 48 for music. You can change this from the Unreal.ini file. Each playing sound effect, ambient sound, and music channel uses CPU time. Therefore, we recommend keeping the number of sound effects audible to the player fairly low, and keeping music channel usage "lean and mean". Hardware-mixed sound: 3D sounds are spatialized by whatever the hardware supports. For example, Aureal pans it, phase shifts it, and applies a complex convolution and bandcap filter to model positional modulation of the sound by the head and ears. The sound system is limited to X channels of hardware mixed sound (where X depends on the kind of hardware, and can be from 6 to 64 for existing sound hardware). Any sounds for which hardware acceleration is unavailable are emulated in software using the software mixer, and thus may sound different (less spacey) than the same sound played on hardware. Each level has a default song and CD track which is played throughout the level. You can specify the song in UnrealEd in "Options/Level" in the "Audio" tab. Music can be transitioned dynamically via a SpecialEvent object hooked up to a trigger or any other event source. Music is not zone based, because that would become annoying when backtracking through maps and in network play. Music is tracked per player so it can be used equally well in single player and network play. The audio subsystem includes a six-tap sound reverberation filter which enables you to customize the echo and reverb effects on a per-zone basis (there can be up to 64 zones in a level, so you can have quite a bit of variety in the audio postprocessing within a level). When you add a ZoneInfo actor into a zone, you can set the following properties: bReverbZone: True to enable reverberation effects in the zone; False to disable them. [this is outdated, but the quick version is: the other properties are 6 reverb tap delays and gains] You can experiment with reverberation filters quickly by going to Options/Level, setting the reverb effects for the entire level, then double- clicking on sound effect names in the sound browser. We only support 16-bit sound output. We tested 8-bit sound output and the quality was unacceptable low: when you mix 64 channels of sound into an 8-bit output stream, you effectively get 2-bit sound effects. 2-bit sound effects are Not Good. The sound system supports both the legacy WinMM sound support, and DirectSound. DirectSound generally achieves the lowest latency, while WinMM works on Win95 machines which don't have DirectSound, and WinNT. The sound code makes heavy use of MMX to improve mixing quality and speed. You get about a 2X performance and quality boost on Pentium processors with MMX technology. On non-MMX machines, the sound code makes some quality/speed tradeoffs by limiting sound effects to having only 64 volume levels. You can hear this limitation by setting up an ambient sound effect with a high radius in an otherwise quiet area: the discrete steps between volume levels are quite audible.