EMU_CHAN_TREMFRQ
emu_wrptr(sc, ch, EMU_CHAN_TREMFRQ, 24); /* 1 Hz */
emu_wrptr(sc, v->vnum, EMU_CHAN_TREMFRQ, 0);
emu_wrptr(sc, v->vnum, EMU_CHAN_TREMFRQ, 0);
emu_wrptr(sc, ch, EMU_CHAN_TREMFRQ, 24); /* 1 Hz */