With U2 producers Flood and Howie B in tow, the band rearranged the bridge section and recorded some new vocals on “Last Night on Earth,” which will likely be the next single from its new album, “Pop.” U2 also oversaw the mixing of a duet by singer Bono and Sinead O’Connor. It is slated for inclusion in the soundtrack to “The End of Violence,” a new film by German director Wim Wenders.

Both songs found Harris assisting Flood and Howie B in marathon sessions that, in one instance, lasted until 6 in the morning. The U2 production team also spent two days working with Harris at the studio, sans the band.

“I wasn’t sure what to expect,” said the mustachioed engineer, whose credits include albums by San Diego’s Cindy Lee Berryhill, Earl Thomas, Peter Sprague, Big Mountain and Mike Keneally.

“For all I knew, they would come in and have the attitude you’d expect people of that stature to have. But Flood and Howie were very down to earth, and seemed very happy with the studio. They were funny, and joked a lot.”

But when U2 arrived, Harris noted, the mood changed immediately.

“The lighthearted atmosphere disappeared and was replaced by serious concentration,” Harris said. “Bono walked right up and said, ‘Hi, I’m Bono.’ I said ‘Hi, I’m Mike.’ Then they started working on the song for the film, and Bono seemed to do most of the talking. Larry (Mullen, U2’s drummer) made some comments; Adam (Clayton, bassist) said very little. (Guitarist) The Edge was interested in what was going on, but not critical. Mostly, Bono and the producers decided things.”

Bono and The Edge subsequently recorded new vocal parts for “Last Night on Earth,” and Harris was impressed with how quickly the two nailed their parts. He was surprised that Bono used an inexpensive, hand-held Shure Beta 58 microphone, and that the singer cut his vocals using live speakers in the control room, rather than in the studio with headphones.

“They told me Bono hates to wear headphones, and this is the way he felt comfortable,” Harris said.

U2 and its manager, Paul McGuiness, returned the night after the band’s concert here to hear the new version of “Last Night on Earth.” At one point, the band listened to a cassette tape of the song in their chauffeured town car. The four musicians then stood outside the studio discussing the song, in clear view of customers parking at the adjacent Coco’s Restaurant.

U2 was charged the same rates as any local San Diego band, according to Harris. But few, if any, local bands have ever booked the studio for four days, around the clock.

“When they left, Bono shook my hand,” Harris said. “And he told me, ‘We’ll have to tell people about this nice studio in San Diego.’ I was very pleased. And I was surprised he would say that, since they have access to the biggest studios in the world.”