Re: [Denemo-devel] began real transposition script

[Richard Shann]

On Fri, 2008-11-07 at 10:37 -0600, Jeremiah Benham wrote:
> I began writing a real transposition script
> 
> (define chromatic_notes '(
>   ("a" 0)
>   ("b" 1)
>   ("c" 2)
>   ("d" 3)
>   ("e" 4)
>   ("f" 5)
>   ("g" 6)))
> 
> (define sharp_list (list "a" "ais" "b" "c" "cis" "d" "dis" "e" "f"
> "fis"
> "g" "gis"))
> 
> (define transpose
>   (lambda (note modulate)
>     (list-ref sharp_list (+ modulate (car (cdr (assoc note
> chromatic_notes)))))))
> 
> 
> Am I on the right path with this. 
I am not so sure that this is a good way to go. A transposition is not
defined by a single integer. 
You need two, one would be the number of diatonic steps, the other
something to encode the number of additional sharps/flats.

So c->cis would be (0, 7)
an augmented unison (that is going for example from C-major to C#-major)
c->cis'' would be (16, 7)
same plus two octaves
while
c->des would be (1, -5)
 a minor second (going for example from C-major to Db-major)

my guess is that someone will have sorted out a neat way of calculating
the amount to add/subtract to the enharmonic_shift for a given
transposition - a good place to look might be the LilyPond source
tarball. 
hth
Richard