MEASURE FOR MEASURE.(the art of conducting symphony orchestras)

The American conductor Robert Spano raised his eyebrows and his baton, and the Atlanta Symphony Orchestra dug into a smoky, "Bolero"-like dance. He was nearing the end of two tense and fatiguing days of recording a new opera, "Ainadamar," in the orchestra's concert hall, a half-buried concrete box. The base of his spine twitched to the beat, as if jolts of current were running through it. He grinned at the cellos, giving them a quick thumbs-up, and cued the trumpets by pretending to flick a cigarette butt at them.

When the music stopped, his body kept going. In the seconds before the next take, he accompanied his instructions to the players with a rapid series of gesticulations that even a musician sitting out of earshot could have understood. He made as if to squeeze an orange. (The message: "Give me a succulent tone." ) He then mimed sliding a toy car down a ramp ("But don't drag; push right into the next beat"), whisking eggs ("Keep the sound vibrant"), and swatting a Ping-Pong ball ("Give the phrase a sharp, light bounce").

A white telephone next to his podium rang, and Spano listened as the opera's composer, Osvaldo Golijov, dictated some changes in the score. Golijov, along with a producer and a few engineers, was sitting in a windowless room backstage, linked to the auditorium by speakers and a TV monitor. "We've never done it that way before, but O.K.," Spano said amiably; a decade of working with Golijov has taught him that a new piece of his is not a fixed object. The conductor hung up and instantly translated Golijov's comments into a command. "A little more schmeary," he told the violins, dragging his open palm through the air, as if he were slathering a dozen bagels with cream cheese. When the red "Record" light, suspended above the orchestra, turned on, the dance instantly became more fluid, the melody sexier: less clop, more sway.

Spano is a small, perpetually quivering man of forty-five, with wire-rimmed glasses, a crescent of hair at the back of his head, and the searing gaze once cultivated by Weimar intellectuals. Spending time with him is both invigorating and exhausting. When he can bring himself to sit down, his leg bounces; his speech careers between erudition and profanity. "Fuck you very large" is one of his favorite expressions, and after using it he is apt to burst into hacking guffaws.

On the podium, Spano marshals this jerky urgency and uses it to kindle the orchestra. "Each conductor enters the music through some key technique," Bruce Kenney, a horn player, told me. "Some conductors are happy when we play together and in tune--precision comes first. Other conductors base their interpretation on the pacing, the tempo, and the energy. Other conductors want a particular sound. Robert's an energy guy."

I first met Spano a decade ago, after he had been appointed music director of the tottering Brooklyn Philharmonic and gave one performance after another in which rattling excitement overcame the often scrappy playing. I particularly relished a rough but light-filled performance of scenes from Olivier Messiaen's cathedral-like opera, "Saint Francois d'Assise."

When the recording of "Ainadamar" was finished, Spano, whose coiled alertness had never flagged, retreated to an underground suite with Golijov, the soprano Dawn Upshaw, and a crowd of singers, Latin percussionists, and orchestra administrators for some celebratory drinking. Spano poured himself shots of vodka and playfully toasted his colleagues. It took more than an hour for his adrenaline to ebb.