Re: Adding parallel thirds to the notes of a melody

[Aaron Hill]

On 2019-04-02 11:15 pm, Gianmaria Lari wrote:
> The following "test" function adds parallel thirds to the notes of a 
> melody:
>
> \version "2.21.0"
> scale = {c d e f g a b}
> test  =
> #(define-music-function (music) (ly:music?)
>    #{
>      \partCombine $music \modalTranspose c e \scale $music
>    #})
>
> \test {\voiceOne a b c'}
>
> I don't have lilypond programming experience and I would like to know:
>
> - if there are hidden mistakes
> - if it is better to write the function in a different way
> - how I could avoid to write \voiceOne in \test {\voiceOne a b c'}
> - how I can encapsulate scale, inside the "test" function

In keeping with my predilection for over-engineering, here is my take on 
your function:

%%%%
\version "2.19.82"

autoParallel =
#(define-music-function (root scale target music)
  (ly:pitch? number-pair-list? ly:pitch? ly:music?)
  (let* ((rscale #{ \transpose c $root { $@(map
           (lambda (x) (ly:make-pitch 0 (car x) (cdr x))) scale) } #})
         (transposed #{ \modalTranspose $root $target $rscale $music 
#}))
    (if (ly:pitch<? root target)
      #{ \partcombine $transposed $music #}
      #{ \partcombine $music $transposed #})))

pentatonic = #`((0 . 0) (1 . 0) (2 . 0) (4 . 0) (5 . 0))

{
  \autoParallel c \major e \fixed c' { e8 f g d e d c4 }
  \autoParallel e \minor g, \fixed c'' { c8 d e fis g4 e4 }
  \autoParallel bes \pentatonic f' \fixed c' { f4 g16 bes c8 d4 f16 g 
bes,8 }
}
%%%%

This is a little more verbose in usage, but it lets you easily specify 
which scale you want using the built-in scale definitions (e.g. 
\mixolydian, \phrygian, etc.) or by creating your own as demonstrated.

It also detects whether the harmony will be above or below and will 
\partcombine appropriately.

NOTE: I only use 2.19 currently, so I still have to write \partcombine 
instead of \partCombine.


-- Aaron Hill

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