input/new/transposing-pitches-with-minimum-accidentals-smart-transpose.ly

   1 \version "2.11.61"
   2 \header {
   3   lsrtags = "pitches"
   4   texidoc = "This example uses some Scheme code to enforce enharmonic
   5 modifications for notes in order to have the minimum number of
   6 accidentals.  In this case, the following rules apply:
   7
   8 @itemize
   9 @item
  10 Double accidentals should be removed
  11
  12 @item
  13 B sharp -> C
  14
  15 @item
  16 E sharp -> F
  17
  18 @item
  19 C flat -> B
  20
  21 @item
  22 F flat -> E
  23
  24 @end itemize
  25
  26 In this manner, the most natural enharmonic notes are chosen.
  27 "
  28   doctitle = "Transposing music with minimum accidentals"
  29 }
  30
  31 #(define  (naturalize-pitch p)
  32   (let* ((o (ly:pitch-octave p))
  33          (a (* 4 (ly:pitch-alteration p)))
  34     ; alteration, a, in quarter tone steps, for historical reasons
  35          (n (ly:pitch-notename p)))
  36     (cond
  37      ((and (> a 1) (or (eq? n 6) (eq? n 2)))
  38       (set! a (- a 2))
  39       (set! n (+ n 1)))
  40      ((and (< a -1) (or (eq? n 0) (eq? n 3)))
  41       (set! a (+ a 2))
  42       (set! n (- n 1))))
  43     (cond
  44      ((> a 2) (set! a (- a 4)) (set! n (+ n 1)))
  45      ((< a -2) (set! a (+ a 4)) (set! n (- n 1))))
  46     (if (< n 0) (begin (set! o (- o 1)) (set! n (+ n 7))))
  47     (if (> n 6) (begin (set! o (+ o 1)) (set! n (- n 7))))
  48     (ly:make-pitch o n (/ a 4))))
  49
  50 #(define (naturalize music)
  51   (let* ((es (ly:music-property music 'elements))
  52          (e (ly:music-property music 'element))
  53          (p (ly:music-property music 'pitch)))
  54     (if (pair? es)
  55         (ly:music-set-property!
  56          music 'elements
  57          (map (lambda (x) (naturalize x)) es)))
  58     (if (ly:music? e)
  59         (ly:music-set-property!
  60          music 'element
  61          (naturalize e)))
  62     (if (ly:pitch? p)
  63         (begin
  64           (set! p (naturalize-pitch p))
  65           (ly:music-set-property! music 'pitch p)))
  66     music))
  67
  68 naturalizeMusic =
  69 #(define-music-function (parser location m)
  70                                         (ly:music?)
  71                         (naturalize m))
  72
  73 music = \relative c' { c4 d e g }
  74
  75 \score {
  76   \new Staff {
  77     \transpose c ais { \music }
  78     \naturalizeMusic \transpose c ais { \music }
  79     \transpose c deses { \music }
  80     \naturalizeMusic \transpose c deses { \music }
  81   }
  82   \layout { }
  83 }