+@lilypond[quote,verbatim,relative=2]
+\time 3/4 % auto beam on 1/4 note groups
+a16 a a a a a a a a a a a a a a a
+\time 12/16 % no defined auto-beaming for this time sig
+a16 a a a a a a a a a a a a a a a
+\time 3/4
+a16 a a a a a a a a a a a a a a a
+\set Score.timeSignatureFraction = #'(12 16) %keep 3/4 beaming
+ % due to beatLength
+a16 a a a a a a a a a a a a a a a
+\set Score.beatLength = #(ly:make-moment 1 8) %beam on 1/8 notes
+a16 a a a a a a a a a a a a a a a
+\set Score.beatLength = #(ly:make-moment 1 16)
+\set Score.beatGrouping = #'(3 4 2 3) %beam on 3/16, 7/16, 9/16, 12/16
+a16 a a a a a a a a a a a a a a a
+@end lilypond