Chopin, Schumann, Liszt and other 19th-century romantic composers expanded the use of register, texture and tone quality to define their music, rather than depending on notes and rhythms, Charles Rosen, professor of music at the State University of New York at Stony Brook and holder of the 1980-81 Norton Chair in poetry, told an audience of 500 at Paine Hall yesterday.

The world renowned pianist-author, who in this first of a series of six lectures discussed the "romantic" approach to music that developed during the 1830s, said 19th-century composers had a "fuller conception" of the sounds they wrote than earlier composers.

Illustrating his lecture with frequent trips to the piano, Rosen first demonstrated the difference between written music and the sound produced when that music is played. Both Bach and Beethoven wrote work in which written notes are inaudible but cause the listener to "imagine the links between notes," he said.

Rosen played excerpts from Beethoven's third piano concerto and a Chopin waltz to show the difference between the romantic and classical use of the piano pedal. Whereas Beethoven used the pedal "only as a special effect to reinforce motifs and dynamics," romantic composers considered the removal of the pedal a special effect, he said.

During his one year stay at Harvard, Rosen, who won the 1972 National Book Award for "The Classical Style: Haydn, Mozart, Beethoven," is teaching a fall seminar on "Music of the 1820s"