Re: Harmonics in tablature

[Lukas-Fabian Moser]

Hi Valentin,

> This is a certain limitation in how the harmonicByFret-Function works. It will 
> calculate the pitch for the given note, thus the Noteheads are automatically 
> placed onto higher strings. Thus you eighter will have to manually specify the 
> string number, or you might do something like in the appended file, which is 
> modifying the harmonicByFret-function to automatically use the proper string. 
> This should work at least for open strings, for artificial harmonics this is 
> not really a problem, since harmonicByFret sucks for that anyway.
>

Thanks much! I think the problem is more complicated than that, or my lack of understanding more fundamental than that.

With your modification, the output now is:

which is _not_ correct since all the harmonics should be played on the third string. (At least on violin/cello its perfectly common to play harmonics in the "upper" half of the string, hence with "fret numbers".) On the cello, I get the sounding pitches from the lower staff by playing harmonics on the 12th, 7th, 5th fret all on the same string. (I hope it's clear that I speak of imaginary semitone frets on a cello.)

1) I think your function

    \set minimumFret = #(ly:pitch-semitones
                         (ly:prob-property
                          (calc-harmonic-pitch (fret->pitch (number->string 12))
                                               (make-music 'NoteEvent 'pitch (ly:make-pitch 0 0)))
                          'pitch))

is just a complicated way of writing \set minimumFret = 12:

(fret->pitch "12") looks up the partial that you get by touching the "12"th fret - which is 1st partial (hardcoded in #fret-partials) - and then translates this into a pitch-delta from c'; this yields #'(1 0 0) (hardcoded in #partial-pitch) which means c''. Hence, you basically call (calc-harmonic-pitch pitch-c'' pitch-c'). This yields c'', hence the call of pitch-semitones returns 12.

2) Now, calc-harmonic-pitch (which seems to have been written by Carl 10 years ago, so I'm very glad he chimed in already) seems to me to be basically a variant of \transpose, for instance:

\version "2.21.0"

chp =
#(define-music-function (p m) (ly:pitch? ly:music?)
   (calc-harmonic-pitch p m))

mus = \relative c' {
  c4 d e f g
}

\new Staff { \chp f' \mus }

(But, as I already remarked yesterday, I think that calc-harmonic-pitch does not work correctly for chords in \relative music:

\version "2.21.0"

chp =
#(define-music-function (p m) (ly:pitch? ly:music?)
   (calc-harmonic-pitch p m))

mus = \relative c' {
  c4 <d g'> e f g
}

\new Staff { \chp c'' \mus }

If this is expected behaviour, then at least I do not understand it.)

3) Ok, assuming that my diagnosis is correct and you actually just achieve \set minimumFret = 12 (at least it's obvious that your code does not depend on the parameters given to harmonicByFret): This shouldn't be what we need, I think, because we explicitly asked for frets no. 7 and 5, respectively. We shouldn't force a minimum fret, but a string number.

4) All of this makes so little sense to me that I'm sure I suffer from some fundamental misunderstanding of the way the harmonics implementation is supposed to work. I have no idea why LilyPond, when we minimumFret to 12, created a harmonic note on the string above with fret number smaller than 12.
So I probably should ask: Is my understanding correct that printing <7> on a certain second string in a tablature diagram should mean that this string should be played with an open harmonic with finger on the 7th fret?

Lukas