About DLS/XMF Format for Mobile Devices (Mobile DLS)
The Mobile DLS Specification defines a wavetable instrument representation format optimized for use in mobile applications. The recommended practice also includes the use of the XMF Meta File Format (version 2.0) to package the DLS data with SMF data into a Mobile XMF file used for the complete musical performance.
Mobile DLS is based on the DLS-2 file format and supports both DLS-1 and DLS-2 technologies through the use of mechanisms introduced in the DLS-2 specification. Mobile DLS departs from previous DLS specifications in a few notable ways, including:
- The technical distinction between melodic programs and percussion programs no longer exists. There is now a single bank + program space, and any bank + program address can hold either type of program. (ulBank bit 31 no longer treated as part of bank + program address.)
- Wavetables are no longer limited to 16-bit or 8-bit linear PCM. There is an extensible mechanism allowing the use of other encodings besides linear PCM, including compression codecs.
- It is possible to implement a Mobile DLS device without DCF and Vibrato LFO, however such an implementation will not be able to play instrument content that is authored to require those features.
- Minimum device requirements including polyphony and system sampling rate have been relaxed due to the limitations of mobile devices. Reverb and chorus have been made optional, and all voice allocation decisions are left to the implementor.
- Harmonization with SP-MIDI SMF content, including a requirement for a General MIDI or General MIDI 2 instrument set.
- Harmonization with Mobile XMF compound content (SP-MIDI SMF plus Mobile DLS instruments).
- Several corrections to the DLS 2.1 text in regard to the DCF, connection transform curve specifications, note exclusivity, and other matters, which
will subsequently be adopted for DLS 2 as v2.2.