Silent Partner to Big Voices By Catherine Spangler and Leslye Davis Man Behind the Music: Kuk Harrell, a vocal producer for singers like Justin Bieber and Rihanna, reveals his process for coaxing superstar performances out of his clients. LOS ANGELES - Two days before Justin Bieber's 18th birthday he was, as usual, working. He walked into the main control room at Record Plant, a recording studio here, his blue-and-pink high-top Balenciaga sneakers unlaced, nodding his head to a sinuous beat blaring over the speakers. On this Tuesday night in February Mr. Bieber was a few weeks into recording his second full-length album, "Believe" (RBMG/Island). The studio was crowded with songwriters trying to turn that beat into a hit; with Mr. Bieber's relatives, in town for his birthday; with a security guard; with various assistants. Then there was Kuk Harrell, the only person not openly vying for Mr. Bieber's attention, who moved through the scrum quietly, every so often checking settings on a computer. Mr. Harrell is Mr. Bieber's vocal producer, filling a many-layered and amorphous job: part vocal coach, part cheerleader, part sound engineer, part therapist. At this studio he's a star, too: the nameplate on a kick scooter at the front desk just says, "KUK." Pop music's universe of celebrities has widened in recent years to include producers and songwriters; they're as crucial to what you hear on the radio as the stars, and increasingly known to the public. But there are deeper levels of highly specialized talent, just as integral, that often go unrecognized. Mr. Harrell, 47, is one of those figures, shaping the sound of radio from the shadows. His client roster also includes Jennifer Lopez and Rihanna, and his job is to make sure that the star's vocal is as powerful and flawless as it can be. That happens in parts. In the studio, rarely, if ever, does a star sing a song the whole way through. Instead Mr. Harrell builds a gleaming whole from granular bits. A singer working with Mr. Harrell covers a few bars - a line or two, maybe four - over and over, with different emphases and inflections, until Mr. Harrell hears what he wants. The process repeats for each section. Only later, after the singer is gone, does Mr. Harrell stitch the best pieces together, Frankenstein-like, into the song you hear. On this night Mr. Bieber retired to a smaller studio in the back of the building to work on "Sunday Morning," an aching midtempo ballad, warming up by singing long stretches of the song. But once Mr. Harrell sat down at the computer, they broke "Sunday Morning" down into small vocal bites, with Mr. Bieber sometimes echoing what Mr. Harrell sang to him moments before. All the while Mr. Harrell's eyes remained fixed on the computer screen, where each new take was represented in ProTools, the production software, by a jagged line, like heart-rate tracings on an EKG, inside a brightly colored rectangle. The data were piling up. Stitching the Best Bits Vocal production can be a tedious task, requiring patience, indulgence and discipline. Mr. Harrell's work begins long before his client shows up, as he determines what kinds of microphone, preamplifiers and compressor will be best. When the singer is ready, he kicks into high gear. "I'll take it in chunks," Mr. Harrell explained, sitting in his all-white apartment the day before the Bieber recording session. "If they sang it amazing, I'll get the first chunk and go, "Oh that was beautiful." Boom. I'll drag that up. The process then repeats. "So I'll begin to search through all the playlists I have of that "moment" and go, "Ah, there it is," then I'll drag that moment up into the comp" - the compiled vocal - "and so on. All the way down, until I get to the end of the record and have a complete final comp. In the studio he's enthusiastic but calm, direct and not sycophantic. Lean and slight, he's got a high hairline and long curtain of hair that recalls the comedian Katt Williams. Most of the time he's at the computer, a cap often pulled low over his eyes, his back upright and rigid. Even though he's seated, he appears to be on tiptoes.