Mahler almost always provides a dedicated staff for the double basses, and this already says a lot. Brahms does not yet, and the DBs remain very constrained to the role of simple reinforcement of the bass line. In Mahler's symphonies, the issue is a bit different, and Mahler very often uses the DBs as a "downward extension" of the cellos, ... not bad, great Gustav. Meanwhile, I want to emphasize that when Mahler wants a "unison" between cellos and basses, he writes the DBs an octave higher than the cellos, so that the result is truly unison and not an octave. However, the DB in the orchestra never fully emancipates itself and, even in Bartók's Concerto for Orchestra, or in Stravinsky's ballets, or in R. Strauss's tone poems—even if naturally, besides no longer being written in pairs with the cellos but on a dedicated staff, it is used much more and often autonomously (but always together with the others)—the DB "disappears" when particularly virtuosic passages appear (unless, naturally, playing them together with the cellos, obviously). The reasons, at this point, are primarily of a timbral nature: the double bass has a timbre and an extension that, in the low register, makes it difficult to perceive sounds accurately (and on the other hand: try executing a fast passage in the extreme low register of a piano: even there it is not so easy to make sense of anything...), so it is clear that a wise composer cannot fail to take this crucial aspect into account. To such an extent that Beethoven himself takes advantage of it (let me jump back) and exploits the "noisy" role of the DB (forgive the double bassists if they are reading). In the "Pastoral," during the "Storm" at letter C of the score, B. divides cellos and basses: the cellos play repeated quintuplets, the basses quadruplets. The passage represents the arrival of the storm, thunder in the distance, a storm approaching: down there there is nothing melodic, and the concomitance of quintuplets and quadruplets makes the whole thing even more "muddled": B. knew this very well and, never like this time, he used an objective limit, transforming it into a timbral effect (here one can truly speak of "orchestration"!). Another indispensable example, but, due to its characteristics, highly emblematic, is the DB solo (all of them! not just one as is still often heard performed) in the 3rd movement of Mahler's First Symphony. That solo, of eight bars (Frère Jacques in D minor), exploits a high register (and not very comfortable?) of the double bass, and we must also assume that in the years when Mahler wrote that symphony, that passage was truly daunting for double bassists; another example of how to "make necessity a virtue," namely a solo that recalls a folk motif, originally joyful, re-proposed in a bleak and grim minor key, entrusted to the double basses in the high register where they undoubtedly sounded poorly intonated due to lack of familiarity with those positions, and where the DB has a decidedly nasal and "empty" timbre. Call him foolish... Excuse me, while I'm at it and since the subject passions me, I'll add one thing that has nothing to do with DBs, but which came to mind regarding solos entrusted to instruments in their most uncomfortable registers. An equivalent example that must be made is the beginning of Stravinsky's Rite of Spring. Today the bassoon plays (almost) well and has lost any hint of uncertainty, bad sound, or hesitation in the vast majority of performances. Bassoonists know that it is a solo they must be able to do. But we are in 2012 and exactly one hundred years have passed. To Stravinsky, many years after he had written the Rite, someone said: "See, Maestro? Finally bassoonists can now perfectly execute that extremely difficult solo, despite the high register!" and Stravinsky replied: "If I had ever imagined it, I would have written that solo a fifth higher!". Do you get the point? He wanted it to sound bad and he wrote the solo in a register that, at that time, was almost taboo for bassoonists (imagine what must have happened at the first performance: I'm sure they threw chairs!). Since we were talking about orchestration, here: I consider these things to be categorized under "orchestration," whereas when talking about Mozart, the discussion is so embryonic that, if it weren't for the eternal dilemma of whether the two terms are synonyms or not, I would simply speak of "instrumentation," understood as the distribution of the forces at play, nothing more and nothing less."