Most concertgoers find it difficult to determine the nature of the relationship between orchestra members and their conductor. Either they seem to be ignoring him, or he seems to be confusing them.

Last Friday at a rehearsal for tonight's Harvard-Radcliffe Orchestra concert, conductor James Yannatos added words to his baton gestures and shed light on this apparent mystery: I got a glimpse of the conductor qua taskmaster.

He sometimes upbraided specific sections of the orchestra to humorous effect, wrangling with the horns, bickering with the percussion and yelling at the flutes.

Yannatos' demanding ideas about how the music should sound often paid off immediately-in strauss' Don Juan, a phrase which had to his ears fallen flat ("it sounds like the thing got stuck in bubblegum") was then hewn to near-perfection, ushering in an exhilarating moment that should stick out in tonight's performance.

Strauss' early masterpiece, finished by the time he was 25, was written under the spell of Wagner's Tristan und Isolde, and takes its cues from the tristesse (and orchestrational largesse) of that monster. In the version Strauss sought to depict, it is not a statue-come-to protagonist's own self loathing that brings on the brimstone. You can look forward to otherworldly brass writing and overwrought, saturated textures. For a first course, it is heavy fare.

The highlight of the concert, and presumably its biggest draw, will be HRO Concerto Competition winner Christina Castelli '00, who has to perform the Sibelius Violin Concerto for herds of "Junior Parents," including her own.

For Castelli, a double-threat who won an international viola competition in 1997, nervousness is probably not an issue. Castelli has been praised in the Washington Post for her virtuosity and for "cantabile resonance," something the Sibelius calls for in spades.

This concerto existed in a rougher, more Beethovenian perform before the Finnish composer excised some blocky, thorny passages from the first movement. There is still plenty of muscular music in the 1905 version we hear tonight, which makes greater demands on the soloist in terms of smoothness and tone. In rehearsal only the first two movements were heard, apparently because of Yannatos' temper, but two were enough to show Castelli at the top of her game. Awesome voicing, awesome dynamic range, and some Heifitzian melodrama suggest a Sibelius not to be missed. For those inclined to adduce parallels, note the resemblance between the second movement of the Sibelius and the refrain of the Gershwin song "Not For Me."

The The last piece on tonight's program is Walter Piston's Third Symphony, a warm, polished, slightly reticent work. The HRO's brass section, sometimes dicey, was wonderful here in rehearsal and Yannatos' tough love made its staccato playing even better. The slow turns of the oboe at the outset have an Italianate flavor (Walter's grandfather was named Antonio Pistone) and the tonal language is cosmopolitan: Piston, luckier than most Harvard seniors, won a Paine Traveling Fellowship after graduation. You'll want to listen in the third movement for exuberant music that Dr. Y wants to deliver in "band style."