The two harp works, by contrast, are indeed soloistic compositions — in effect, mini harp concertos. But whereas the monothematic Ravel is typically virtuosic in nature, Debussy's two dances are entirely given to pastel picture painting. He borrowed some elements from the obscure Portuguese composer Francisco de Laceda (1869-1934), whose piano music delved into Portuguese folk sources. Danses is often mistaken as having a Greek influence, but if that's so, both Laceda and Debussy were influenced by dreams of an ancient Greece. The second dance is, on the other hand, definitely a waltz of the relaxed sort popular in late 19th and early 20th century France.

Pleyel, the French piano firm, commissioned the Debussy dances to illustrate the virtues of its then new chromatic harp, which had all 12 notes of the chromatic scale. That eliminated the need for pedals to change the chromatics when a piece shifted keys. Pleyel dabbled in assorted instrumental experiments during the early 20th century: a more brilliant type of harpsichord for Wanda Landowska; and mechanical instruments of several types, not least the player piano and piano rolls. The company even made the earliest piano rolls of Stravinsky playing his own orchestral music from the keyboard — and quite well, too. The catch is that having a chromatic harp rendered the harp glissandi, so dear to Impressionist composers, impossible. Therefore it quickly fell into disuse. (Too bad, for that would have spared us the sound that composer Roger Sessions famously dubbed "harp vomit.")

Thus Debussy's 1903 Danses contain no glissandi, whereas Ravel's piece — commissioned by the rival harp manufacturer Erard, seeking to retain the traditional harp mechanism — is overloaded with glissandi. The harpist keeps sliding his fingers up and down the strings like a cat on a skateboard over ice. In that sense, these two most frequently programmed harp works are as much about the harp as for it.

Ravel's two-part Introduction and Allegro is also typical of his compositions for solo instrument with orchestra. Of course, there aren't many by Ravel. Except for the three-movement G-Major Piano Concerto — the one using both hands — they are all based in some manner on the basic form of the Romany (aka Gypsy) rhapsody. The others include Tzigane for violin and orchestra and the notoriously bravura Concerto in D Major, using only the pianist's left hand. (Pianist Robert Casadesus once noted that, "With the other hand the pianist is praying, to hold on to reality for dear life.")

All these first three pieces received fine performances. The Roussel Trio got off to a mildly ragged start but soon caught the breeze into smooth sailing. Harpist Rado, a faculty member at the San Francisco Conservatory, was especially resonant and clear of sound. But whereas those were "fine" presentations, the mounting of the Ravel Quartet was sensational. Every little detail was perfectly in place and meticulously balanced. I've rarely heard this overprogrammed quartet so admirably played. Violinists Reiss and Elbert Tsai, violist Emily Onderdonk, and cellist Ruth Lane deserved every decibel of their ovation.

I cannot seem to attend a chamber music concert these days without the Ravel Quartet on the program. I have the impression that were I to give a good slap to some sleeping string player, shouting "Ravel Quartet!" as I did so, their hands would automatically start fingering and bowing the piece even with no instrument in sight. That also means that frequency of encounter requires a high standard if the quartet is to make any impression at all. Sunday's performance did. I've been haunted by the slow movement ever since.