A furious few help break the hypnotic, bass-heavy sound

WHEN veteran rapper E-40’s wildly infectious single “Tell Me When to Go” became a hit in early 2006, it turned the urban music industry’s spotlight on hyphy, a cultural movement created in Oakland that had been bubbling in the underground for several years.

Hyphy music is characterized by up-tempo beats accented by thunderous bass and a reliance on quirky keyboard effects. It’s highly repetitive (even by rap standards) and tremendously hypnotic. Where the similar crunk style of rap often comes off as an all-out assault on your senses, hyphy tends to be a bit more inviting because of less abrasive supporting sounds, sometimes including melodic keyboard passages and speedy drum patterns.

Producer Rick Rock is the sonic architect of hyphy. An accomplished Sacramento-based beat-smith who has also worked with E-40, Jay-Z and Fabolous, among others, Rock in 2004 released on Virgin Records his group the Federation, whose “The Album” featured seminal hyphy cuts “Hyphy,” featuring E-40, and “Go Dumb.”

Even though the album failed to make much of a commercial splash -- it has sold just more than 26,000 copies, according to Nielsen SoundScan -- the Federation is regarded as a leader of the hyphy musical movement because of its association with Rock and because of the Bay Area success of the “Hyphy” single. The group signed with Warner Bros. this year and is slated to release its second album in September.

Keak Da Sneak, another prominent hyphy artist, is a guest vocalist on E-40’s “Tell Me When to Go,” and the scratchy-voiced Oakland rapper churns out material at a pace that rivals Pearl Jam’s output of live albums. “That’s My Word,” one of several albums he put out in 2005, contained the Bay Area hits “Super Hyphie” and “Hyphie.” His awkward delivery styles and innovative phrasing make him a distinctive, memorable performer who raps over both hyphy and conventional rap beats.

After making a name for himself in the early 1990s by defining and popularizing the mob music sound (a slow, keyboard-driven offshoot of Los Angeles’ funk-inspired gangster rap), Vallejo-based E-40 has helped popularize the hyphy sound by recording with a number of up-and-coming rappers. In addition to his work with the Federation, in 2004 E-40’s Sick Wid’ It label released “The Street Novelist,” an album from rapper Turf Talk that included the Rick Rock-produced single “It’s Ah Slumper.” The percolating song, featuring E-40 and the Federation’s Stressmatic, was one of the most popular songs in Bay Area rap clubs during its peak.

E-40’s “My Ghetto Report Card,” which includes “Tell Me When to Go,” contains a number of quality hyphy songs as well as several crunk cuts. Lil Jon has helped up the album’s profile by releasing it on his BME Recordings through Warner Bros. A stark black-and-white video for “Tell Me When to Go” gave a firsthand look into the hyphy scene, making it tangible for fans.