Time signature with alternate in parentheses

In polymetric music, a composer may indicate beat structure by following one time signature with another in parenthesis, for example, ‘3/4 (6/8)’ indicating a 6/8 beat in a 3/4 measure, or ‘6/4 (6/8)’ indicating a 6/8 beat in a 6/4 measure.

This snippet provides a small Scheme wrapper around the \compound-meter markup function that can be used to override the TimeSignature stencil, displaying both a regular and an alternate time signature.

\version "2.24"

#(define ((time-parenthesized-time t tp) grob)
   (let ((m1 (grob-interpret-markup
              grob (markup #:compound-meter t)))
         (m2 (grob-interpret-markup
              grob (markup #:compound-meter tp))))
     (ly:stencil-combine-at-edge
      m1 X RIGHT
      (parenthesize-stencil m2 0.1 0.4 0.4 0.1)
      0.3)))


\relative c' {
  \once \override Staff.TimeSignature.stencil =
    #(time-parenthesized-time '(3 4) '(6 8))
  \time 3/4 b8 b8 gis8 gis4 gis8 |
  \once \override Staff.TimeSignature.stencil =
    #(time-parenthesized-time '(4 4) '(3 2 3 8))
  \time 4/4 b4. b4 b4.
}