NDS_BGMFILER 2009/07/05 released.
Music creation application for the DS.
Author homepage (Japanese)
GBAtemp download
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Music creation application for the DS.
Notable Japanese homebrew author MeRAMAN has released a new version BGMFILER for the DS, it has not really been covered before (first version was released in early October 2008) but it is a music making application for the DS focussing on "midi" type files (the actual format is BDT but wav and midi support was added throughout development).
It features midi playback (and for a handheld very good conversion), a keyboard able to use many instruments (inbuilt and external), channel selection along with many ways to vary how things are played back.