As the deepest instrument in the orchestra along with the contrabass tuba, the contrabassoon generally plays one octave below the bass voice. It is used mainly in the octave between C1 and C2 (Brahm’s Symphony no. 4 in E Minor, 3rd movement). It provides the bass foundation both in unison with the bass and contrabass instruments and an octave below the bass instruments.
In the past it was very occasionally used for thematic and solo tasks, too, between C2 and C3 and between C3 and C4.
Since the 20th century it has been entrusted with solo tasks more often (e.g., by Maurice Ravel, Alban Berg and Benjamin Britten).
Contrabassoon + woodwinds
The contrabassoon in combination with the bassoon an octave above sounds completely homogeneous. Contrabassoon with the bass clarinet an octave higher sounds full and mellow.
Contrabassoon + brass instruments
Contrabassoon + tuba an octave higher produce a mighty and full sound that is capable of carrying an orchestra tutti. It can also play in unison and in octaves with the trombones, although here the sound is harder and more precise; if the sound is strongly forced the contrabassoon can only add shading.
Contrabassoon + horn: good combinations with the low horns. Together with the tuba playing an octave above it, the contrabassoon provides the bass for the horns’ chordal harmonies.
Contrabassoon + strings
Contrabassoon + double-bass in unison produce a substantial, full composite sound. Good combinations with the cellos playing an octave higher.