MusicTimeSignature

MusicTimeSignature[numerator]
MusicTimeSignature[numerator, denominator]
MusicTimeSignature[numerator, denominator, beatLength]
MusicTimeSignature[properties]

represents the meter of a musical container.

MusicTimeSignature[4, 4]
MusicTimeSignature[6, 8]

The available properties are "Numerator", "Denominator" and "BeatLength".

signature = MusicTimeSignature[6, 8];
signature["BeatLength"]

Attach a time signature through a container property:

MusicMeasure[
  {"G4", "A4", "B4"},
  <|"TimeSignature" -> MusicTimeSignature[3, 4]|>
]

Different measures in one MusicVoice may use different time signatures.

See the Wolfram Language reference for simple and compound meter behavior.