NEW ORLEANS, La.--When Tortoise [ tickets ], the adventuresome Chicago-based quintet, left the stage at the Howlin' Wolf around 1:15 a.m. on Friday morning (6/15), four and a half hours had passed since the evening of music had begun.

Four acts had crossed the stage, Tortoise being the headliner, and two increasingly prominent pop-music trends had been on display: the rock band minus a lead singer, and the laptop computer as musical instrument.

Tortoise was the most low-tech of the night's performers. However, the group's center-stage instrumentation--a xylophone and a vibraphone--is certainly more exotic to pop audiences than the array of portable electronics employed by the night's three opening acts--Mouse on Mars, Nobukazu Takemura and Vert. More on them later.

Those mallet instruments were used in almost every song, most excitingly when done so in tandem, as they were on the song "Blackjack," a selection from Tortoise's most recent album, "Standards" (Thrill Jockey), throughout which they percolated with a giddy, thoughtful effervescence. The pulsing rhythms intertwine and form a kind of aural grid of soft percussion. That grid lends structure to Tortoise's music, providing a playing field in which the other members of the group have their fun.

Otherwise, Tortoise uses the basic tools of rock (drums, guitars, keyboards) in the construction of its intricate compositions. But the musicians don't use them traditionally. The group is as rambunctious as it is curious.

Not one of the band's five members stuck with a single instrument for longer than a song or two's duration. Doug McCombs and Jeff Parker alternated on guitar and bass, and Parker's decision to remain seated for most of the show helped to emphasize chamber-music associations.

The three remaining members, John McEntire, Johnny Herndon and Dan Bitney, built up a sweat, trading duties on, among other things, keyboards and drums--there was always a drummer playing, sometimes two, a la the Grateful Dead and the Allman Brothers, of whose jam legacy Tortoise represents the more esoteric fringe.

The crowd greeted almost every Tortoise song with hoots and cheers, recognizing opening riffs. Though many audience members attempted to dance--the music is danceable, despite the group's reputation for brainy innovation--most listened attentively. Seeing Tortoise live provides an opportunity to peek into the machinery behind its complicated studio albums. On this occasion, the live renditions didn't hold up to the recorded ones, but judging by the enthusiasm of the audience, a lack of musical epiphanies was a small price to pay for practical enlightenment: who plays what, how particular sounds are produced, etc.

Tortoise has no singer, but Bitney, impish and ever-smiling, seemed genetically predetermined to satisfy the audience's need for a center of attention. He was always up to something, shaking a tambourine, fiddling with a gadget, gazing proudly at his fellow musicians. McCombs--who, like all of Tortoise, plays in other bands, in his case the more standard rock act Eleventh Dream Day--painted with the broadest strokes; he often filled the concert hall with deeply reverberating guitar lines, reminiscent of the sounds that composer Ennio Morricone used to evoke the American west in his soundtracks to movies such as Clint Eastwood's "The Good, the Bad and the Ugly" and "Fistful of Dollars," movies that featured silent heroes.

Not quite a co-headliner, the German trio Mouse on Mars preceded Tortoise. Mouse on Mars excited the audience in a visceral way with which none of the night's other musicians even tried to compete. The band includes technicians Andi Toma and Jan St. Werner, plus drummer Dodo Nkishi. Toma was the evening's one rock star. He wore a black T-shirt featuring the group's logo, smoked cigarettes continuously, and pounded on a low-down bass guitar when he wasn't tweaking samples with a small electronics setup positioned at the front of the stage. The clean-cut St. Werner played Gallant to Toma's randy Goofus, politely addressing the audience on occasion, and patiently plying a considerable amount of keyboard and computer equipment. Nkishi sang a little, albeit through enough digital equipment to turn his voice into something reminiscent of the Chipmunks.

Anyone possessing even a passing familiarity with Mouse on Mars' recordings would have been surprised by the performance. Much of the group's catalog consists of dense but dreamy synthesized atmospheres. Live, though, the group rocked, occasionally resembling New Orleans' own Nine Inch Nails, heavy on the downbeat and unambiguous in its intent to get the audience dancing. To that end, it succeeded, even if the subtleties of albums like "Iaora Tahiti" were missed.

Mouse on Mars was preceded by two soloists who used laptop computers--indeed, the very sort of machine on which you are likely reading this review--to alternately entertain and mystify the slowly assembling audience.

First up was a German musician called Vert. His laptop produced a series of dewy sounds with a rhythmic buoyancy, which he complemented by playing lullaby-like melodies on a keyboard. Only a heartless Luddite would have failed to enjoy the pleasure that Vert took in his performance, as he eagerly manipulated noises with his computer.

Early arrivals no doubt included cognoscenti eager to hear Japanese musician Nobukazu Takemura, one of the most accomplished electronic artists working today. Seated in front of three laptops, two of them stark white fetish-objects projecting the Apple logo, he was as self-contained as Vert was extroverted. His performance came in two portions: first, a haunting, slowly building ambient soundscape that might accompany a Michael Mann film, followed by a decidedly up-tempo pop number.

Laptop music, with its emphasis on the unexpected uses of personal technology, carries the implicit question of what the rock of the future might sound like. Takemura provided an answer of sorts, by featuring an unintelligible computerized vocal, which lent his pop tune an Esperanto-like flavor. No translation was offered, and no one in attendance seemed to mind.