Re: MIDI rendition of things like rall./acc./rit./fermata

[Flaming Hakama by Elaine]

David,

On Mon, Jun 14, 2021 at 6:46 PM David Kastrup <dak@gnu.org> wrote:

>
> You saw the followup?


Well, it seems I missed the follow up.
Glad to see the functional approach.


> The one with
>
> tempoChange =
> #(define-music-function (interval endscale thenscale music)
>    (ly:duration? scale? (scale? 1) ly:music?)
>   "Make a gradual tempo change over @var{music}, essentially changing
> speed after
> every duration of @var{interval}, approaching a factor of speed of
> @var{endscale}
> compared to the start.  Afterwards, tempo is switched to @var{endscale} of
> the
> original speed (default 1).  If @var{endscale} is 0, the speed reached at
> the
> end is just maintained and can be overriden with an explicit @samp{\\tempo}
> command if required."
>    (define (scaletempo oldscale newscale)
>      (make-apply-context
>       (lambda (ctx)
>         (set! (ly:context-property ctx 'tempoWholesPerMinute)
>          (ly:moment-mul (ly:context-property ctx 'tempoWholesPerMinute)
>                  (ly:make-moment (/ newscale oldscale)))))))
>
>    (let* ((muslen (ly:moment-main (ly:music-length music)))
>           (intlen (ly:moment-main (ly:duration-length interval)))
>           (steps (/ muslen intlen))
>           (endfactor (scale->factor endscale))
>           (thenfactor (scale->factor thenscale)))
>      (make-simultaneous-music
>       (list music
>             (context-spec-music
>              (make-sequential-music
>               (let loop ((rsteplst (iota (1+ steps) endfactor (/ (- 1
> endfactor) steps)))
>                          (res (if (positive? thenfactor)
>                                   (list (scaletempo endfactor thenfactor))
>                                   (list))))
>                 (if (null? (cdr rsteplst))
>                     res
>                     (loop (cdr rsteplst)
>                           (cons* (scaletempo (cadr rsteplst) (car
> rsteplst))
>                                  (make-skip-music (ly:make-duration 0 0
> intlen))
>                                  res)))))
>              'Score)))))
>
> in it?
>
> --
> David Kastrup
>


Things I would suggest to consider:

Since this is presumably making several tempo changes in succession, I
think that singular "tempoChange" is a bit misleading.  Isn't \tempo
already a tempo change?   I would suggest "tempoTransition".

Some parts of this usage are a bit confusing.  If I am slowing from 4=104
to 4=92, as a user of this function, I am supposed to do the math and enter
whatever the ratio 92/104 is?  (Or, I have to write a  scheme expression to
do the calculation)?  Seems like it would be easier and clearer to just
specify the resulting tempo, and let the function do the math to figure out
the ratio.

It would be helpful to document the variable "thenscale".  Perhaps you used
"endscale" instead of "thenscale" in some places in the comments?

I am not sure I understand the notion of fiddling with the final tempo.  In
general, specifying a tempo is for the music that follows.  So to specify a
tempo change and then have to do something else to maintain that tempo
seems like extra.  I can see that if you are going back to a Tempo, such a
feature might seem useful.  But in those cases, aren't you also going
(assuming you are doing both MIDI and PDF) going to add \tempo "a Tempo"
anyway?


Thanks.


HTH,

Elaine Alt
415 . 341 .4954                                           "*Confusion is
highly underrated*"
elaine@flaminghakama.com
Producer ~ Composer ~ Instrumentalist ~ Educator
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