 Haydn's piano trios are essentially piano sonatas with the violin and cello playing mostly supporting roles, doubling the treble and bass lines of the piano score.But Mozart gives the strings an independent role, using them as a counter to the piano, and adding their individual voices to the chamber music conversation.Mozart introduced the newly invented clarinet into the chamber music arsenal, with the Kegelstatt Trio for viola, clarinet and piano, K. 498, and the Quintet for Clarinet and String Quartet, K. 581.