I'm programmer of WTD.
I can understand a little english, sorry.
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FMPSG's WonderSwan sound is made WonderWitch (Qute Co.,Ltd.).
Music data is made mml of "vsound.il"(sound driver).
It have compatibility "sound.il" (default sound driver of WonderWitch.)
They can not use WonderSwan emulator. They need WonderWitch.
(Bacause these sound driver use BIOS of WonderWitch.)
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About other FMPSG's WonderSwan sound, they are made WTD.
WTD do not need WonderWitch and WonderSwan.
WonderSwan emulator can use WTD.
(WonderWitch can use WTD, too.)
How to use (WonderSwan emulator):
http://homepage1.nifty.com/~sha_w/wtd/emulate/
(Japanese, and sample mml.)
(1) make MML file
please write mml by text editor.
(2) compile to WTD's music file
"WTC.COM" is mml compiler.
please D&D mml file.
(This process is making music data of the WonderWitch.)
(3) convert to ROM-image file of WonderSwan Emulator.
"WSMAKE.COM" is ROM-image maker.
please D&D music file.
ROM-image can use some WonderSwan emulator (oswan, etc..).
Moreover, Audio Overload can play the WTD's music data converted to ROM image when extension of filename were changed from "WSC" to "WSR".
About the WonderSwan's I/O (sound), please see
http://www16.atwiki.jp/soundfile/pages/21.html
(Japanese)