Woodwind instrument pitched two
octaves below the soprano
clarinet and one
octave below the
bass clarinet. Uncommonly used, and not really sold anymore, the
contrabass clarinet normally simply plays off the bass clarinet parts, which ocassionally have split parts (raising the contrabass's notes an octave so that they sound at the same pitch as the bass's) for just such a situation.
The contrabass has a lower range approaching that of a tuba, but its tone is softer and mellower than the tuba's brassiness. One could serve as a reasonable substitute for a string bass (aka double bass), however. Provides excellent low-bass for a clarinet ensemble.