In modern times, the most common clarinet is the B clarinet. However, the clarinet in A, pitched a semitone lower, is regularly used in orchestral, chamber and solo music. An orchestral clarinetist must own both a clarinet in A and B since the repertoire is divided fairly evenly between the two. Since the middle of the 19th century, the bass clarinet (nowadays invariably in B but with extra keys to extend the register down to low written C3) has become an essential addition to the orchestra. The clarinet family ranges from the (extremely rare) BBB octo-contrabass to the A piccolo clarinet. The clarinet has proved to be an exceptionally flexible instrument, used in the classical repertoire as in concert bands, military bands, marching bands, klezmer, jazz, and other styles.