\version "2.19.10"

#(define (ledger-line-no middle-C-pos p)
   "Returns the number of ledger-lines a pitch @var{p} will have with
middle C position @var{middle-C-pos} expressed as staff-steps from the
middle staff line."
   (let* ((ps (ly:pitch-steps p))
          (mid-staff-steps (- middle-C-pos))
          (top-line (+ mid-staff-steps 4))
          (bottom-line (- mid-staff-steps 4))
          (above? (> ps top-line))
          (below? (< ps bottom-line))
          (steps-outside-staff
           (cond
            (below? (- ps bottom-line))
            (above? (- ps top-line))
            (else 0))))
     (truncate (/ steps-outside-staff 2))))

octavate =
#(define-music-function (parser location threshold mus)
   (integer? ly:music?)
   "Create an ottava for notes which have at least @var{threshold} ledger lines"
   (let ((elts (ly:music-property mus 'elements)))
     
     ; Put an "ottava 1" in front of the first NoteEvent
     ; such that pitch will result in more than one ledger line
     ; Put an "ottava 0" in front of the first NoteEvent
     ; such that one or fewer ledger lines are needed.
     ; start-loco? and start-ottava? are flags which ensure that
     ; only the first pitch qualifying for an ottava 0 or 1, respectively,
     ; receives 'OttavaMusic
     
     (define (build-new-elts mus-expr new-expr start-loco? start-ottava?)
       (if (null? mus-expr)
           new-expr
           (let ((p (ly:music-property (car mus-expr) 'pitch)))
             (cond
              ((not (ly:pitch? p))
               (build-new-elts
                (cdr mus-expr)
                (append new-expr (list (car mus-expr)))
                #t #t))
              ((and (ly:pitch? p)
                    start-ottava?
                    (>= (ledger-line-no -6 p) threshold))
               (build-new-elts
                (cdr mus-expr)
                (append
                 new-expr
                 (list (make-music 'OttavaMusic 'ottava-number 1))
                 (list (car mus-expr)))
                #t #f))
              ((and (ly:pitch? p)
                    start-loco?
                    (< (ledger-line-no -6 p) threshold))
               (build-new-elts
                (cdr mus-expr)
                (append
                 new-expr
                 (list (make-music 'OttavaMusic 'ottava-number 0))
                 (list (car mus-expr)))
                #f #t))
              (else 
               (build-new-elts
                (cdr mus-expr)
                (append new-expr (list (car mus-expr)))
                #t #t))))))
     
     (make-music 'SequentialMusic 'elements (build-new-elts elts '() #t #t))))

%%%%%%%%%%% EXAMPLE %%%%%%%%%%%%

music = {
  a''8 b'' c''' d''' e''' f''' g''' a'''
}

{
  \music \bar "||"
  \octavate #1 \music \bar "||"
  \octavate #2 \music \bar "||"
  \octavate #3 \music \bar "||"
  \octavate #4 \music \bar "||"
}