In both Halion and NotePerformer, the playback for the bass trumpet in E-flat sounds an octave plus a major sixth lower; but it should sound only a major sixth lower. Is there a way to change this instrument’s octave transposition? I’m looking at the Endpoint Setup dialog, but I’m not sure how to change the octave there (or even if I should try).
Thanks for any suggestions!
Yes: in Play mode, in the right-side VST panel, click on “Edit Instrument” to change the octave in the Halion player.
You can alternatively specify an expression map that provides the necessary octave transposition in Endpoint Setup. (I can’t remember if we have a suitable expression map that transposes in the right direction: if not, it’ll be simple to copy the provided one and invert its transposition.)
This seems to be a problem with the instrument definition in Dorico, not than the playback libraries.
For concert pitch, the bass trumpets play an octave below the written pitch. Whether that is “correct” might be a matter of opinion, but the difference between transposed and concert pitch goes to the wrong octave for the Eb bass, but is correct for the Bb bass.
So IMO the “logical” place to work round this is with a clef change using the octave transposition property, not by tweaking the expression maps or sample players.
FWIW having recently input some Wagner that included bass trumpet in Eb, I didn’t notice that the playback pitch was in the wrong octave. Some more research of Wagner’s (often weird) ideas about brass notation might be called for… 
There are several other ways to handle this.
Thanks for the suggestions! I agree with Rob, I think the instrument definition has the wrong octave for the Eb bass trumpet. I fixed it by putting in a new treble clef and using its Octave shift property, which I didn’t know about (it’s awesome).
Yes, Wagner’s notation for brass gets pretty crazy with the transpositions; I once sprained my French horn brain trying to practice the prelude to the third act of Lohengrin. Thanks again!
After a bit of digging, the saga of the bass trumpet in the Ring cycle is crazy. Part of the problem seems to be that Wagner had at least two different ideas about making a new instrument or using a newly invented one, none of which came to anything. (And his first idea wasn’t a trumpet at all, but a saxhorn.) The final result was that the score was variously in C, D, and Eb, but the instruments that were actually built and used were in C, Bb and A.
Several respectable authorities seem to have (wrongly) deduced what the instrument might have been (i.e. pitched an octave lower than it actually was) based on the scores - so at least I was in good company unwittingly making the same mistake as people like Forsyth!
I checked our instrument definitions, and we have the tenor E flat trumpet transposing down a sixth, and the bass trumpet transposing down an octave and a sixth. Is that not correct?
Here be dragons. Apparently, in 1821 the Allgemeine Musikalische Zeitung reported a first performance on a “Chromatische Tenor-trompetenbass” invented by Heinrich Stölzel (who a few years before had invented a valved horn). Take you pick whether you translate that as a tenor or a bass trumpet!
It seems that in the early 19th century there were two different Eb trumpets pitched as Daniel described (with 6-foot and 13-foot tube lengths), but the 13-foot version was only used in military bands and later became extinct.
So I’m not sure whether we should change our default instrument definition, really.
I think it is pretty clear that the orchestral “Bass trumpet in Eb” has only ever been the 6-foot version, notwithstanding Wagner’s attempts to confuse the issue.
What Dorico should do about the fact that there was an obsolete instrument with the same name pitched an octave lower is beyond my pay grade 
So you would propose we raise the pitch of the bass trumpet by an octave, and remove the now-identical tenor trumpet?
I’m encountering my Eb bass trumpet part in Stravinsky’s Rite of Spring, which is more recent than Wagner; so for what it’s worth, I’d recommend changing the instrument definition.
But maybe leave the Eb tenor trumpet as is? I’m not at all a military brass band expert, so I would defer to anyone who knows more.
I would say the “standard” orchestral notations for bass trumpet are in Eb C or Bb transposing down a 6th, octave, or 9th.
Presumably you have some authority for the tenor trumpet but like Stephen I have no idea what it is or was. The only credible-looking reference I found on the web was a page which started “The bass trumpet, sometimes called the tenor trumpet… .”
There was also an instrument maker’s website listing “herald trumpets” (with valves followed by a straight tube) in various sizes labeled soprano, tenor and bass (all in B flat) and a bass in G (!!!) but there was no statement about the pitch or tube lengths, so who knows what octave they play in.
I’m ignoring websites claiming to sell “tenor trumpets” with pictures that are obviously tenor trombones
The fanfare trumpets can also include a high Eb (sop cornet pitch), and an F (at french horn pitch) (I have a set…). I’ve never seen an Eb an octave and a sixth down of any kind.
Daniel, perhaps a good compromise would be to have two variants of the bass trumpet (much like you have two variants of the piccolo – C and D-flat), with the two variants labeled either by how they transpose or by their tube length. I’m agnostic about what to do with the tenor trumpet.
In my experience, the designation tenor trumpet never appears (even if of course I do not have knowledge of every instance of low e flat trumpet in all literature ever – and indeed, as suggested above, there may well be ensembles other than the symphony orchestra that employs an instrument known as a tenor trumpet). It is bass trumpet in e flat or in b flat (more rare in c).
The e flat bass trumpet reads a sixth higher than sounding pitch, not an octave and a sixth as Dorico generates. I suggests this is changed.