LOS ANGELES -- When rapper Sen Dog chose to leave Cypress Hill in late 1995, he wasn't entirely sure if he would return, he said.

Having lost his focus on the hip-hop band he'd co-founded in 1988 with lead rapper B-Real and DJ Muggs, Sen said he needed to wake himself up. But now that he's back in Cypress Hill, helping inspire the release of their fourth album, IV (Oct. 6), Sen seems to have a better perspective on the future, not to mention the past.

"I just felt like I had to do something exciting again," said the Cuban-born Sen, 32, of his decision to step away from the crew. "Cypress Hill had kind-of gone systematic, and the communication just wasn't there at the time."

Sen (born Senen Reyes) apparently found what he was looking for by developing his heavy-metal project SX10, who currently are gearing up to record their full-length debut for Flip Records.

While his Cypress crewmates Muggs and B-Real are on a European promotional tour, Sen is hanging at home in Los Angeles. Clad in a Public Enemy T-shirt, the stocky rapper sat on a large green chair positioned in front of a television in the office of Flip Records. Sen changed channels as he talked -- sometimes without glancing at the screen -- but seemed eager to discuss his return to Cypress Hill.

"Now, knowing what I know and doing what I've done and coming back into the group and being a productive part of it, I think the whole time I spent away from the band was good, not just for me, but for Cypress as well," Sen said.

It may sound strange that Sen has returned to Cypress Hill just as SX10 are about to hit the studio, but the rapper said he doesn't see it that way. Explaining that his priorities will shift from group to group in accordance with demand, Sen said it feels totally right to be back in hip-hop's most marijuana-friendly group.

Though its predominant themes remain dope-smoking and violence, IV abandons the gloomier tone of its recent predecessors, 1993's Black Sunday and 1995's III (Temples of Boom), while exhaling fresh grooves, funky beats and artful, ace production work.

"Checkmate Fool," for instance, hangs onto a steady bassline while B-Real's nasal snarls counterbalance Sen's thick baritone in classic Cypress style. "It's a fun song, an aggressive song, and that's what I love about Cypress this time around -- the aggressiveness of it, the funk of it, the depth; that it's danceable but yet it's certified hip-hop," Sen said.

IV has several songs that offer sharp twists on the Cypress sound. For instance, "Tequila Sunrise" overlays a smooth groove with Latin textures and horns. "From the Window of My Room" showcases Muggs' adventurous spirit as a producer, as it allows classical violin to provide as much groove as do the hip-hop beats. And "When Lightning Strikes" sports a heavy guitar riff.

"When I heard that, I couldn't believe it," Sen said of "Lightning Strikes." "I was like, 'Whoa, that's heavy.' That's the kind of stuff I want to do. I don't want to follow [pop-rapper] Puffy's recipe for success. I don't want R&B girls singing on my rap record ... I just want to be Cypress."

When he performed again with Cypress Hill on this summer's hip-hop-heavy Smokin' Grooves tour, he said he noticed a difference in the crew's energy. "There's just a whole new intensity about the group now," Sen said. "When we record, when we do shows, we're having fun ... like it was before the corporate thing came in."

Though his bandmates never recorded an album without him, Sen came in midway through the recording of IV and appears on seven of the album's songs.

Cypress Hill fans contacted through fansites said that Sen's return is pivotal to the band's future. "It wouldn't be Cypress without Sen Dog," wrote Kevin Schick, 20, of Los Angeles. "That album's gonna be the bomb. With all the sh-- that's out there now that people are thinking is hip-hop, hip-hop needs Cypress Hill back in the game, front and center."

Cypress Hill burst onto the scene with their 1991 self-titled debut, receiving initial support from college radio before taking off and eventually hitting the multi-platinum mark. With such song titles as "Light Another," "Legalize It" and "Hits from the Bong," Cypress Hill's pro-pot stance has remained a pivotal theme in their music.

A tale of a prolific weed-grower, the new tune "Dr. Greenthumb" begins with the ominous question, "Have you ever had the problem of running out of weed and just can't find some anywhere?"

Sen said he doesn't mind that Cypress may be more famous for advocating marijuana than for their music. "You've got to be remembered for something," he explained.

Despite their words to the herb, Sen said that the most important element of IV is that it's the product of his excitement and freshness after he re-infiltrated Cypress Hill.

"We didn't feel like doing another 'Insane in the Brain' song, like the label might have wanted us to do," he said, referring to their massive 1993 hit.

"We thought that we really needed to start fresh. Whatever we've done in the past, f--- it! That doesn't mean sh--. We're coming out now, brand new again. That's what it felt like in the studio, and that's what the album feels like."