>I wasn't planning to implement Set Filter because it seems to mainly be
>used to change the brightness of the Amiga's LED (rather than for the
>muffling effect it also has on the Amiga, but not on PC players, e.g.
>Modplug and Winamp), so I think it's ok to ignore it on the GBA. Is it
>implemented in other GBA players?
I've implemented it in MASO System, yes.
http://maso.r0x.free.fr