I visited the Spoleto Festival USA for the first time in 1984, and I've come back as often as I could thereafter. I can remember many magnificent performances (Gian Carlo Menotti's 1991 staging of Mozart's "Nozze di Figaro" with a radiant young soprano named Renee Fleming haunts me still) and, yes, a few tepid ones. But never, until Tuesday afternoon at the Simons Center Recital Hall, had I encountered an unexpected masterpiece by a contemporary composer of whom I'd never heard.

Say it plainly — Michael Harrison's "Revelation: Music in Pure Intonation" (2005) is probably the most brilliant and original extended composition for solo piano since the early works of Frederic Rzewski three decades ago (and no, I am not forgetting Elliott Carter). What could have been a mere glossary of unfamiliar sonorities made possible by Harrison's unconventional tuning of a grand piano turned instead into a virtuosic tour-de-force that would have done credit to the hypothetical team of Franz Liszt and Claude Debussy working overtime.

Harrison, born in 1959, studied at the University of Oregon and the Juilliard School and then later with Indian musician Pandit Pran Nath. He has collaborated extensively with two other composers fascinated with alternative tunings, La Monte Young and Terry Riley.

But, with all due respect to Young and Riley, pathfinders both, Harrison seems far more comfortable with the ramifications of this musical language than they do, in rather the same way that children who grew up with computers and the Internet always will put their parents to shame in technical matters.

There is nothing didactic about his music: it simply flows with the sort of effortlessness that is possible only after a great deal of effort has been expended.

This is not the time or place for an extended comment on what has come to be known as "just intonation" (you may find a lengthy definition, complete with musical examples, on the Web site run by the composer and critic Kyle Gann, located, appropriately, at www.kylegann.com).

In the same way that the technical innovations of, say, Arnold Schoenberg or Milton Babbitt are of interest to fellow musicians but pretty much irrelevant to the general public's appreciation of their work, I think that the best way to encounter Harrison's work is simply to dive into it.

"Revelation" begins with a gentle, nocturne-like exploration of the scales and intervals that Harrison will explore in the 75 minutes to come. The music initially seemed so terribly pretty, with its dewy sonorities, meditative calm and heavy pedaling, that I feared Harrison might be venturing into "New Age" territory (so vividly described by Thomas Pynchon as "mindbarf drooling from the speakers" in a California mall).

But no, there is intellectual rigor here throughout, and Harrison proved a bravura pianist. And if my mind wandered every now and again, it was always to a place it had never been before.

By the end of the afternoon, in a spectacular finale, Harrison was hammering the keys of the piano with his whole arm, but by then we had become so used to his sounds that we sank into them as though they were soft pillows.

I laughed aloud at the glissando that he traced so delicately from the bottom to the top of the piano, which called to mind a delicious shiver up the spine. Soon all was drone, overtone and reiterative patterns until an ocean of sound seemed to be pouring out of the piano, the walls, the floor, the heavens.

And then Harrison stopped playing, but the pedals were still down and the piano took on a palpable aural afterglow as the sonorities began to dissipate. Unfortunately, a few people began to applaud immediately after the composer lifted his hands from the instrument, which broke the spell prematurely (on the recording of "Revelation," the resonance goes on for almost a minute after the last note is played).

Silence is as important to music as sound, and to have a silence that had been so hard won snatched away so quickly counted as a minor heartbreak.

My debt to John Kennedy, the conductor, director and host of Spoleto's "Music in Time" series, who brought this extraordinary music to Charleston, is enormous.

He will present two more programs this season: a concert of contemporary Asian music tonight and music by Per Norgaard and Phillip Bimstein on June 3.

Harrison's own work is available on disc or via amazon.com download, as I recently discovered. I am listening to "Revelation" as I type these words, and it works almost as well over headphones in a hotel room as it does in a concert hall.

On Bach and Buxtehude

To arrive on time for the program of J.S. Bach and Dietrich Buxtehude at St. Matthew's Lutheran Church Tuesday night was to arrive too late, for the only seats that were left were in the back row of the balcony, where it is impossible to see the stage.

Nevertheless, it was gladdening to see so many people there for this beautiful music and I learned my lesson for further offerings at this venue.

I stayed long enough to hear soprano Courtney Budd sing one of Bach's early cantatas, "Mein Herz Schwimmt in Blut" (BWV 199) with an abbreviated version of the Spoleto Festival USA orchestra under the direction of Andrew Megill.

Budd sang with a welcome mixture of tonal purity, musical intelligence and emotional intensity, a lovely artist. I also admired Megill's conducting, which was fleet, gently propulsive, musicologically informed but never fussy.