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Re: Separating pitch and rhythm

From: David Kastrup
Subject: Re: Separating pitch and rhythm
Date: Wed, 21 Mar 2012 19:54:10 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.94 (gnu/linux)

Siska Ádám <address@hidden> writes:

> Dear List,
> is there an effective way to separate the pitches and the rhythms in a
> voice? I'm thinking about something like defining a variable
> consisting only of rhythms:
> Rhythm = {
>       \time 4/4
>       4 4 4. 8
>       8 8 4 4 8 8
>       2 4 8 8 ...
> }
> and then apply this to different sequences of pitches:
> Seq1 = {
>       \clef treble
>       c d e f
>       g a g f e d
>       c e g c ...
> }
> Seq2 = {
>       \clef bass
>       c b a g
>       f e f g a b
>       c g e c ...
> }

#(define-public (for-some-music recurse? music)
  "Walk through @var{music}, process all elements calling @var{recurse?}
and only recurse if this returns true."
  (let loop ((music music))
    (if (recurse? music)
       (let ((elt (ly:music-property music 'element)))
         (if (ly:music? elt)
             (loop elt))
         (for-each loop (ly:music-property music 'elements))
         (for-each loop (ly:music-property music 'articulations))))))

#(define (extract-all-durations music)
   (map! (lambda (m) (ly:music-property m 'duration))
         (extract-music music
                        (lambda (m) (ly:duration?
                                      (ly:music-property m 'duration))))))

applyRhythm =
#(define-music-function (parser location p r)
  (ly:music? ly:music?)
    (let ((l (extract-all-durations r)))
        (lambda (m)
          (and (pair? l)
               (if (ly:duration? (ly:music-property m 'duration))
                     (set! (ly:music-property m 'duration) (car l))
                     (set! l (cdr l))

Rhythm = {
        s4 s4 s4. s8
        s8 s8 s4 s4 s8 s8
        s2 s4 s8 s8
SeqI = {
        \clef treble
        c d e f
        g a g f e d
        c e g c

SeqII = {
        \clef bass
        c b a g
        f e f g a b
        c g e c

\new PianoStaff
<< \new Staff \applyRhythm \SeqI \Rhythm
   \new Staff \applyRhythm \SeqII \Rhythm

I have written the "for-some-music" function previously but not
committed it since I could not immediately think of an application.  But
it fits the bill here reasonably nicely.

David Kastrup

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