The tuba is a wide, conical-bore brass instrument. This is to say that it is
the bass/contrabass analogue of the bugle or flugelhorn. Historically the tuba
evolved from the ophicleide, which had keys instead of valves but the same wide
bore, which determines its timbre, which determines how it blends (or fails to
blend) with other instruments. The ophicleide was seldom used in the
orchestra, having the intonational difficulties of any keyed brass, but those
problems being much more dangerous to the overall ensemble in the bass.
As the tuba began, from the middle of the 19th century, to take a place in the complement of the full orchestra, it was found to blend with horns (usually the only other conical brass) but not with cylindrical brass (trombones) and neither, disappointingly, with the basses of other families, such as [contra]bassoon and string bass.
On this point, it is extremely instructive to compare Brahms's first and second symphonies. The first uses contrabassoon as bass of the brass choir, conspicuously in the soft chorale in the introduction to the finale, where a tuba would not work at all. The second uses a tuba, but the consequence is to isolate, rather than integrate, the trombones, as we hear at the climax of the first movement's development and also in the very last bars of the work.
This is all by way of approaching the question, what can the tuba really do? That question precedes, and partly determines the approach to, the composition of a work such as this; and the answer is a fairly limited one. What the tuba is unexpectedly good at is "sing[ing] both high and low", in Shakespeare's hilarious phrase. What it is not good at is cutting through a dense texture or overpowering us with sheer volume. Accordingly, the piano part must stay out of the tuba's way, above, below, or around it.
Copyright © 2015 -- 2020 Frank Wilhoit