Percussion instruments play not only rhythm, but also melody and harmony. They can be classified by their musical function. The instruments with definite pitch include the timpani, marimba, tubular bells, xylophone, vibraphone and glockenspiel. The instruments with indefinite pitch include snare drum, cymbals, whistles, bass drum and drum set. The percussion plays a major role in keeping the band on beat, and together, and thus is an important and irreplaceable section. A good percussionist should have a good sense of rhythm and beat.