Hello Lib, this is a limitation of the Lilypond parser which implements the syntax
\tempo [text] [duration = ...]
Here it assumes that ... is an unsigned integer. This I think is not
unreasonable, if you tell a musician to play something in MM 72.4 he will
probably be a bit confused.
Anyway, the solution to the problem would be to simply not use this parser
feature. \tempo is only a parser feature and not a music function as a music
functions do not allow the 4 = 120 syntax and does not allow having two
arguments both of which can be optional but one being mandatory.
But in the end \tempo ... still evaluates to a music event, as you can see if
you do
\displayMusic \tempo "some text" 4 = 120
This creates two music events:
(make-music
'TempoChangeEvent
'metronome-count
120
'tempo-unit
(ly:make-duration 2)
'text
"some text")
is the event that is responsible for creating the tempo mark and
(make-music
'ContextSpeccedMusic
'context-type
'Score
'element
(make-music
'PropertySet
'value
(ly:make-moment 30)
'symbol
'tempoWholesPerMinute))
is what makes midi tempo work (it basically sets Score.tempoWholesPerMinute to
a moment of duration metronome marking * metronome base length, so in our case
120 * 1/4 = 30.
So what you need to do to get non integral is to manually create the first
thing:
{
#(make-music
'TempoChangeEvent
'metronome-count
72.4
'tempo-unit
(ly:make-duration 2)
'text
"Weird tempo")
c
}
To get midi to work you’ll also need to do
\score {
{
#(make-music
'TempoChangeEvent
'metronome-count
72.4
'tempo-unit
(ly:make-duration 2)
'text
"Weird tempo")
\set Score.tempoWholesPerMinute = #(ly:make-moment (* 724/10 1/4))
c
}
\layout { }
\midi { }
}
If you do not what to do the conversion to rationals 72.4 → 724/10 yourself
you can use (inexact->exact ...), but keep in mind that this will include
rounding errors:
(inexact->exact 72.4) -> 2547348539231437/35184372088832
which is the representation of 72.4 with binary digits with machine precision
(the denominator is 2^45).
Cheers,
Valentin
Am Sonntag, 25. Juni 2023, 11:44:59 CEST schrieb Lib Lists:
> Hello,
>
> I realised that Lilypond doesn't like it if the metronome value is a
> non-integer. In the example below, assigning 7 to the voiceAmount
> variable triggers a 'error: not an unsigned integer'. I tried to
> construct the metronome number marking as a markup, but without
> success.
>
> Any suggestions? The idea is to have the metronome markings values
> automatically generated, starting from 4 = 120 in the upper staff.
> Below both a M(non-)WE and the complete example
>
> Thank you in advance for any help!
>
> Cheers,
> Lib
>
> %%% MWE %%%
> \version "2.25.5"
> \score {
> \new Staff {
> \tempo 4 = #(* 1 (/ 120 7 ))
> { c' }
> }
> }
> %%%
>
>
> %%% COMPLETE EXAMPLE %%%
> \version "2.25.5"
>
> voiceAmount = 7
>
> \score {
> \new StaffGroup <<
> #@(map (lambda (i)
> #{
> \new Staff {
> \scaleDurations #(cons voiceAmount i) {
> \tempo 4 = #(* i (/ 120 voiceAmount ))
> \relative c'' \repeat unfold #i {{c c c c }} \bar "||"
> }
> }
> #})
> (iota voiceAmount voiceAmount -1))
>
>
> \layout {
> \context {
> \Score
> \remove Metronome_mark_engraver
> \cadenzaOn
> }
> \context {
> \Staff
> \remove Time_signature_engraver
> \consists Metronome_mark_engraver
> }
> }
> }
> %%%
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