San Francisco Symphony music director Michael Tilson Thomas looks like a laid back conductor on stage: he makes sweeping gestures which sometimes seem (to us, anyway) too vague to contain a beat; often enough, it looks like he's surfing over the musical waves of the orchestra rather than leading them. And he has a genial bonhomie in chatting up the audience to introduce a piece here or there, as Keeping Score shows.

Yet, the musicians play together and the shape of the music comes out wonderfully in full detail; it's a tight ship. So much so that they'll have to expand the mantlepiece for another three Grammy awards for their latest recording of the Mahler Cycle. We just had a phone conversation with MTT, and we now understand there is another side of him: a strictly business, straight to the point, no-fussiness-allowed persona. If what we see on the podium is the velvet glove, there is a strong firm hand underneath that knows how and when to take control.

We were hoping to have a wide ranging state-of-the-symphony conversation, but MTT was intensely studying the score for Charles Ives' Concord Symphony at the time, and kindly but firmly steered us in that direction. Ives is one of his favorite composers, a true American original who was the subject of one of the Keeping Scores episodes. And what a subject: he worked at an insurance company by day, and wrote music in his spare time. Since he had the financial stability of a day job, he did not care about publishing his music or having it performed. He could musically innovate without fearing the wrath of flustered audiences and narrow-minded critics. Eventually the world caught up with his inventions and now Ives is part of the classical canon. His towering achievement is the piano Sonata No. 2, So monumental is the piece that Henry Brant decided to orchestrate the piano score as a symphony for a 100 piece orchestra.This is the version the SF Symphony will play tonight through Saturday, for the very first time.

"Concord, Mass."