Miles Sound System SDK 7.2a

Sound under Xbox 360

Discussion

For digital audio output, Miles for Xbox 360 uses the XAudio system library. Miles only uses one XAudio voice - we do everything else in software for maximum speed (we are much faster than the Xbox system library (which are also software based). We do all of our work on a background CPU, so you can play hundreds of digital samples at once with no CPU hit on the main CPU at all!

The Miles Sound System on Xbox 360 supports uncompressed, IMA ADPCM, MP3, Ogg Vorbis, and XMA digital sound. IMA, Ogg Vorbis, and MP3 are not natively supported by the Xbox, but Miles makes the decompression and streaming to the sound hardware seamless - they just take a little more CPU. For basic performance calculations, playing 32 uncompressed samples takes 7% of the background CPU, playing 32 IMA ADPCM samples takes 10%, playing 32 MP3 samples takes 19%, and playing 32 Ogg samples takes about 35%. The MP3 is so fast due to writing almost the entire decoder in optimized PPC assembly.

The Xbox 360 also supports full 5.1 discrete audio. You can set the volume levels of the 5.1 individual channels with the AIL_set_sample_51_volume_pan or AIL_set_sample_51_volume_levels functions.

The Xbox 360 doesn't have dedicated MIDI hardware, so Miles uses its built-in DLS synthesizer for all MIDI playback. This has the added advantage of allowing you to author custom DLS instrument sets to optimize memory use.

And that's pretty much it - Miles is a piece of cake to use on the Xbox 360.

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Group: Overview for Microsoft Xbox 360
Related Functions: AIL_set_sample_51_volume_levels, AIL_set_sample_51_volume_pan