Clarify handling of tab clef

[Danielku15]

The 6stringTabClef is too large when using a standard 1sp for guitar tablature staves with 6 strings. Also it's not clearly defined on what pitch/line the tab clef is expected to be drawn (staff bottom/center?).

Here a screenshot of staff5Lines+gClef and staff6Linex+ 6stringTabClef.

As you can see, neither alignment nor the height (if you shift up the clef) are correct.

Can it be clarified what staff spacing needs to be used for tab staves? Also it should be specified on which pitch/line the tab clef should be placed by scoring programs.

MuseScore seem to use 1.5sp which I find quite wide. But if that's the expectation according to spec I can scale accordingly to my preference. But I (and likely font authors) need clarity that 1.5sp is used on tab staves.

Same thing for the "tall"/"small" variants of clefs: what staff spacing is expected?

Any help & insights are appreciated 😁

[dspreadbury]

I agree we could do with some clarity in the specification here. The assumption is indeed that the gap between strings in tablature is 1.5 spaces, rather than 1 space. I don't have good bibliographic sources for that convention (I should find some!) but in my experience that rule is consistently applied.

Ideally you should be able to use the same point size for all music drawn at one space size, so that's why a treble clef is sized appropriately for the standard 250 em (font design unit) space size, while the tablature clef is sized appropriately for a 375 em space size.

I'll add some implementation notes to the 'Clefs' range to make this relationship explicit in future.

[Danielku15]

Thanks for clarifying, I'll update my library (alphaTab) accordingly as I'm currently improving SMuFL Spec compliance.

As for the clef alignment: should I just rely on the bBox to visually center the clef?

[dspreadbury]

If you position the Y origin in the vertical centre of the tablature (i.e. between the middle two strings) that should give you the correct placement for the tab clef.

[Danielku15]

Thanks for clarifying. Placing the clef in the middle and choosing between fourStringTabClef and sixStringTabClef depending on the string count. Scaling the clef seem to be a bad choice as paddings to the staff get inconsistent.

With Scaling:

Without Scaling:

Not scaling the clefs seem consistent with Guitar Pro and MuseScore behaviors.

MuseScore:

Guitar Pro 8: