A string quartet is a musical ensemble consisting of four musicians playing two violins, a VIOLA, and a CELLO. The CELLO player is typically the lowest-pitched instrument in the quartet and is responsible for providing the bass line. The VIOLA player is the second-lowest-pitched instrument and is responsible for providing the harmony. The two VIOLIN players are the highest-pitched instruments and are responsible for providing the melody. A violist is a musician who plays the VIOLA, and a bassist is a musician who plays the bass. All five of these musicians are members of a string quartet.