Rock bands have it easy: no one expects them to sound as good as their recordings. The bar is higher in hip-hop, where audiences are far more finicky about drum tones — which is why over the years the standard hip-hop gig has come to amount to, if you’re lucky, two turntables and a microphone. If you’re not lucky, you end up with three guys pissed off at a temperamental DAT player. Rap in its purest elementary form was turntables; but seeing the Roots whip out a snippet of the Sugar Hill Gang’s "Rapper’s Delight," I was reminded that the earliest rap recordings featured studio bands — albeit bands that aped the sound of a DJ spinning records.

The Roots, from Philadelphia, have been around long enough to figure out what works (most of rap’s live ensembles never get that opportunity), and they’ve decided that it’s not wise to stage a live hip-hop performance with fewer than eight musicians. Even then, some of them are multi-tasking. Two MCs, one of whom doubles as a turntable (Rahzel, the Jimi Hendrix of human beatboxing, remains a stunning freak of vocalization). A bassist and two guitarists, one of whom doubles as the group’s only natural soul singer. A keyboardist, who like the rest of the band has memorized large chunks of the hip-hop repertoire spanning several decades. A drummer, and also a percussionist, this last manning a rig that includes bongos and, more important, an electronic drum pad — not a pre-programmed drum machine, which would rob him of spontaneity, but an instrument that allows for such state-of-the-art hip-hop signatures as firecracker snares and Clipse-grade locked-and-loaded shotgun rim shots.

Last Friday night at Avalon, the Roots opened with a number that attested to the possibilities for a hip-hop band. It purported to be "Rock You," from last year’s tour de force, Phrenology (MCA). But they played it like a DJ in the midst of a master mix: it began with the beat from Queen’s "We Will Rock You," cross-faded into the backing track to 50 Cent’s "In da Club," then jumped into N.E.R.D.’s "Rock Star," then into the Roots’ own taut, Grammy-night version of Eminem’s "Lose Yourself," winding up with the Black Sabbath–like guitar onslaught from Run-DMC’s "Raisin’ Hell."

Not everything was quite so invigorating — the Roots are still the Grateful Dead of hip-hop, prone to long tangents and a practiced eclecticism that, though impressive in its reach (Afro-Latin jazz, dub reggae, Hendrixian acid blues, modern soul, Bad Brains–style hardcore), leads inevitably to dull stretches. But you can appreciate their attempt to be everything to everybody — to prove what a hip-hop band are capable of. If they don’t, there isn’t anyone else to pick up the slack.