3 Stem tremolos or rolls are tremolo signs that look like beam segments
4 crossing stems. If the stem is in a beam, the tremolo must be parallel
5 to the beam. If the stem is invisible (eg. on a whole note), the
6 tremolo must be centered on the note.
12 \context Voice\notes \relative c''{
13 \property Voice.Text \set #'direction = #1
14 \property Voice.TextScript \set #'padding = #5
15 a1:4^":4" a:8^":8" c:16^":16" a:32^":32" a^"x" a:^":"
16 a4:4 c:8 a:16 c:32 a a: a2:
25 c,16:32 c: c c a16:32 a: a a