'Dirrty' Work

''I never in a million years expected her to gravitate towards that,'' says Perry. ''And when she did, it was hard for me to let go of that song, because it's really special for me. So the deal was, 'I need to hear how you sing it.' And when I heard her, I said, 'okay.''' But when it came time to record the ballad -- which lays a string arrangement over a Lennon-esque piano part -- Perry was a fierce taskmaster, forcing Aquilera to eschew what Perry calls ''hoo-ha'': elaborate R&B vocal improvisations. ''When she sang it, I tried to keep it straight. I told her to get rid of the finger waves,'' Perry says. ''Every time she'd start going into hoo-ha, I'd stop the tape. I'm like, 'You're doing it again.'''

Perry ended up using Aguilera's guide vocal -- her rough first take -- on the finished song. ''She had a hard time accepting that as the final track. It's not a perfect vocal -- it's very raw,'' says Perry. ''She's a perfectionist. She knows her voice really well, and she knows what's going on. She can hear things that nobody else would catch.'' Still, Perry was able to convince Aguilera to forego perfection in favor of the track's unvarnished emotion; the ''hoo-ha''-free track is one of Aguilera's most restrained performances.

Latin pop to rock The other 18 tracks on ''Stripped,'' many of which were produced by Dr. Dre associate Scott Storch, make the album sound like a genre-jumping mix tape (and a lengthy one at that -- at nearly 78 minutes, ''Stripped'' is longer than ''Exile on Main Street''). The songs range from the Enrique-ready Latin pop of ''Infatuation'' to the pseudo-hard rock of ''Fighter,'' which evokes the Janet Jackson of ''Black Cat.'' In another Linda Perry production, ''Make Over,'' Aguilera sings over a garage-rock beat and surf guitar. Meanwhile, a contrasting number, ''Impossible'' -- written, produced and arranged by Alicia Keys -- would've fit right in on Keys' Grammy-grabbing ''Songs in A Minor.''

The album's long and sometimes difficult gestation process may explain its length and diversity, according to Jamieson; he points out that this is Aguilera's first full-fledged release since her self-titled debut three years ago. ''It took a long time to get focused and to find the material that Christina was feeling good about,'' he says. ''But you can't rush art. Christina is a woman with a vision.'' For better or worse, anyone who's seen the ''Dirrty'' video would have to agree.