Pitch impression on Double Basses
Double basses have a quite unfocussed sound, especially in their very low register. In some occasions, it might be even tricky to actually identify clearly which note they are playing. This occurs on passages where the basses have a quite solistic role. In order to clarify the pitch, they usually get doubled an octave higher by the celli in such situations which add a precise pitch impression to the sound. If there is a (string) chord above the bass note (without heavy degrees of dissonances), doubling is not neccessarily needed as the chord tones will also clarify for our brain which pitch the contrabasses are playing. There are also instruments at this very low register which create a very clear pitch impression due to their harmonic spectrum. Especially the contrabassoon and the contrabass clarinet can produce a very focused sound that low. While the tuba can reach these notes as well, it as well is not that focussed in pitch impression. So depending on what impression you’re after, you should keep these (doubling) alternatives in mind for your orchestration work.