drum samples are clustered around middle C

upside: they sound better.

bonus: only drums that are used in the song are sampled. bigger kits can fit
into the little XM instrument size (8 samples) as long as you only use a couple
of drums from the big kit.

the downside:

unfortunately this change introduced quite a bit of complexity (keep track of
notes used, explicit arbitrary mapping of Bosca notes to XM notes).
Cleanups to avoid problems with leftover patterns
re-start SiON sequencing after rendering
much more accurate sounding

volume, length of bar and most importantly pitch have changed.

I don't understand why SiON's idea of middle C and XM's idea seem to be three
semitones apart. I guess that's my mistake, somewhere.