Open the ROM in ZSNES, go to the level that plays the music, and just before the music starts, press F1 (or whatever hot key it's set to) and select 'save SPC file'.
This is the only way I'm familiar with. There may be a way to in snes9x, but I never tried it.Legacy custom music A site with a non-useless dislike button SMW hacking channel
Assuming you're using ZSNES, just press F1 when the song plays, and there should be an option to save the SPC (can't remember the exact words). As for Snes9x and bsnes.... I have no clue, although it's probably very similar.
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Thanks to all,it worked
In SNES9X, go to File > Save Other > Save SPC Data. bsnes doesn't have an option to save SPCs.
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I'm working on a hack! Check it out here. Progress: 64/95 levels.