Re: Subtracting 128th notes

[Lukas-Fabian Moser]

Hi Stuart,

Am 31.03.22 um 16:30 schrieb Stuart Simon:
> LilyPond Users:
> I'm running into a scenario where it would be useful to subtract three 
> 128th notes from a longer note's duration while having the longer note 
> still appear as a single note in the printed score. This is useful 
> when I have a printed score with three grace notes that I want to be 
> played on the beat rather than before it, but the grace notes are 
> understood differently from both the acciaccatura and the 
> stereotypical "eighth-note with grace upper neighbor plus two 
> sixteenths equals four sixteenths" type of appoggiatura commonly found 
> in Classical-era music. Please do not stop reading this when I tell 
> you that this may be a feature request, for it may also be a simple 
> exercise in finding the right duration scale factor.
>
> When the longer note is a whole note, the case is very simple. The 
> duration is 1 * (1 - 3/128) = 1 * 125/128.
>
> When the longer note is a half note, the case is more complicated. In 
> my mind, the duration  should be 2 * 61/64, but I don't know if that 
> is correct.
>
> Similarly, when the longer note is a quarter note, the duration should 
> be 4 * 29/32.
>
> One more example, this one using a dotted duration. The duration of a 
> dotted quarter note is 3/8 of a measure, so the duration should be 4. 
> * ((1/128)/(3/8)) = 4. * 1/48.
>
> I still don't know if I am correct or not,  but if I am, then it would 
> ease my mind a bit.

You could let Lily do the math for you (if I understand your problem 
correctly):

\version "2.22.0"

reduce-duration =
#(define-scheme-function (minuend subtrahend) (ly:duration? ly:duration?)
   (ly:make-duration
    (ly:duration-log minuend)
    (ly:duration-dot-count minuend)
    (* (ly:duration-scale minuend)
       (- 1 (ly:moment-main (ly:moment-div (ly:duration-length subtrahend)
                                           (ly:duration-length 
minuend)))))))

{
  a$(reduce-duration #{ 1 #} #{ 128*3 #}) e'128 e' e'
  \time 2/4
  a$(reduce-duration #{ 2 #} #{ 4. #}) e'4.
  \time 3/8
  a$(reduce-duration #{ 4. #} #{ 8. #}) e'8 e'16
}

I'm pretty sure there's a much better way to do this and to get a more 
conventient syntax.

The problem with my approach is the following: In principle, we can just 
write

\reduce-duration 1 128*3

but the problem is that this returns a "naked" duration, which Lily is 
not willing to combine with the pitch written before it. For this, you 
need to call the function in scheme mode with $, but then it's not so 
easy to write durations - hence back to LilyPond mode with #{ ... #}.

Lukas