Club soundmen are rarely called on to mix eight turntables, so the crowd gathered at Tramps Tuesday night to see the Elements of Hip-Hop Tour wasn't all that upset about the short delay due to technical difficulties. Indeed, the booing only started when an unnamed MC started rapping before the X-Ecutioners set about a "real freaky bitch" who "comes out at night."

\\For a musical genre still thought of as cutting edge, hip-hop artists and audiences are hyper-concerned with upholding tradition, and talking smack about freaky bitches was not a tradition this particular crowd wanted to uphold. Instead, the Elements of Hip-Hop Tour -- a three-week tour featuring Chicago rapper Common, New York turntablists the X-Ecutioners and Roots member Rahzel -- was all about musical tradition: human beatboxing, spinning the wheels of steel, MC-ing in front of a live band and collaborating with old friends.

\\Rahzel kicked things off with forty-five minutes of beatboxing, eliminating any doubts as to whether the vocal technique can be as subtle and sophisticated as any instrument by simultaneously imitating deep bass lines, chest-thumping kick drums, echoing snare shots and ticking hi-hats. Once establishing a groove, he began, quite unbelievably, to sing or rap over it, thrilling the crowd. His mimicry of vinyl scratching, of turntables slowing down or speeding up, of little dogs barking -- of almost anything -- was so exact and wide-ranging that it seemed he could record an album as dense as "It Takes a Nation of Millions..." with just a four-track.

\\Element number two, spinning records, is the province of the X-Ecutioners (formerly the X-Men until threatened with legal action). Sharing the stage with a group of rappers trading off rhymes on two mikes, the four turntablists unleashed a dense torrent of murky funk reminiscent of Miles Davis' "Bitches Brew." Spinning records is a physical act, and each of the X-Ecutioners wowed the crowd by scratching behind backs and over shoulders, creating a pastiche of unknown and familiar beats and hooks.

\\X-Ecutioner Mista Sinista returned to the stage for headliner Common's set, joining a loose, blues-inflected band of drums, piano, double bass and acoustic guitar. Working the stage in a green, knee-length raincoat and a cap pulled down over his ears, Common ("See-to-the-oh-double-em-oh-en," for spelling enthusiasts) flowed in an easygoing, conversational style while spinning his performance conceit: the Hotel Common, where guests are encouraged to enjoy the myriad moods while respecting their neighbors.

\\Songs at the Hotel Common lasted only a verse or two, which kept the pace fresh and lively, and a guest appearance by De la Soul ended the show on a sustained note of committed collaboration. But Common's best moment occurred during "I Used to Love H.e.r.," about a relationship attenuated by money and fame. Wedging jazzy instrumental choruses between spoken verses, Common and his band elevated their hip-hop, and pointed a way to an organic future by drawing on a shared musical