“American Idol” Top 9. (Michael Becker/Fox)

It’s rock ‘n roll week on “American Idol.” Judge Randy Jackson’s in black patent-leather, Jennifer Lopez is dressed in a beautiful – and surprisingly age appropriate -- white dress, and Steven Tyler has come as the Bronx Zoo Cobra.

As an extra challenge to the chicks tonight, Gwen Stefani is going to costume them in clothes from her L.A.M.B clothing line, whether or not it suits them or their song choice. L.A.M.B. stands for “Love Angel Music Baby,” which, in one of those incredible coincidences which make covering product-placement orgies of excess like “Idol” so stimulating, is also the name of her first solo album.

Jacob Lusk is going to sing Marvin Gaye tune “Let’s Get It On” which, record mogul/Idol in-house mentor Jimmy Iovine and this week’s guest mentor will.i.am predict enthusiastically, will cause a population explosion in nine months

Then Jacob remembers his upbringing. The producers may have planned rock week, but he has a message for them: He’s not going to corrupt the youth of America!

“I can’t get on stage and sing something that’s not me. It’s very blunt. It says ‘Let’s do it – let’s do the nasty’,” Jacob says. So, instead, he’s going to sing Michael Jackson’s sittin’-in-your-shrink’s-waiting-room ode, “Man in the Mirror,” while dressed in an outfit of the purest white. And, Jacob tells the camera in no uncertain terms, if he lands in this week’s Bottom 3, it won’t be because he failed to do a sensational job performing this song. It will be because Americans refused to look at themselves in the mirror.

There’s a word for this -- I wish I could think of it. Oh yeah -- sanctimonious!

Sadly, they did not have time to change Jacob’s choreography after the tune switch. So while he’s telling us to become better people, in order to change the world, and dressed in his blindingly white costume -- he’s doing a bump and grind with his backup singer. Who – turns out – is the song’s co-writer! How cool is that? She’s getting paid to back up Jacob The Sanctimonious – and she’s getting royalties! You go girl! Randy praises Jacob’s “moral conviction,” but show host Ryan Seacrest wonders which was more powerful – Jacob’s voice or his hip thrust. Thank you, Ryan Seacrest.

Haley Reinhart is sick to death of the judges telling her “Janis Joplin this” and “Janis Joplin that.”

“You want Janis – I’ll give it to you!” Haley says. Haley has not stopped to consider that perhaps they were being kind. True, Haley has a raspy voice, something like Janis Joplin’s, and she has frizzy hair, something like Janis. But on the Janis Joplin Meter, she’s a Janis Jo -- or even maybe just a Jan. Haley ka-lumps around on stage in 8-inch heels, dressed in some come-hither L.A.M.B. number, and wearing bright red lipstick. As Joplin rolls over in her grave, JLo tells Haley if she keeps that up she’s gonna “be around for a minute” – which sounds vaguely ominous, but we’ve been assured is not.

The taped rehearsal bits hint at some kind of conflict and confusion around Casey Abrams’s song choice this week. He wants to sing The Police’s “Every Little Thing She Does is Magic,” but Iovine and Will.i. humiliate him out of it (W. compares him to Sammy Davis, Jr. like he meant it to sting). So Casey’s off doing Creedence Clearwater Revival’s “Have You Ever Heard the Rain” instead. Wow – that’s quite a switch. We’ve always hated this tune; even when CCR sang it, it was little more than a musical whine. Casey clearly lacks conviction doing this one; he’s singing at the top of his range and sounds thoroughly uncomfortable. But he’s made one brilliant musical choice: bringing back his stand-up bass, which thoroughly distracts the judges. Either that, or they have just decided to focus on the bass, not the performance, because they saved Casey from getting the hook just two weeks ago and they’re not about to nick him so soon. Randy, in particular, seems endlessly impressed that anyone can sing and play bass at the same time. “Casey is making the upright bass cool – this is revolutionary!” he gushes.

Lauren Alaina sings earthy Aretha Franklin tune “Natural Woman.” So, of course, Gwen Stefani has dressed Lauren like – Gwen Stefani, right down to the ratted birds-nest hairdo. Because nothing says “earthy” like hip, arty, New York fashion. Lauren’s voice carries her through, however. Tyler tells her she’s changed this night from an immature little girl to a “natural born woman” which – we can’t stress enough – is a really creepy thing for a 62-year-old competition judge to say to a 16-year-old female competitor on national TV, even if she is all tarted up in a gingham bustier and ratted hair.

Tyler takes a break to ask Seacrest how the balls on his feet are doing. Randy asks Seacrest if he’s wearing deodorant.

“Are you guys in the same show I’m on right now?” Seacrest wonders, speaking for us all.

Just when we thought rocker James Durbin had gone deep into his Legend in His Own Mind mode, he has the good sense to do George Harrison’s ballad, “While My Guitar Gently Weeps,” bucking discouragement from the two mentors (“That would be while my guitar gently sleeps,’ snarks Jimm.i.ovine). It’s tastefully done with only one big Jamesian crank-it-up at the end. He’s got tears in his eyes at the end of the performance, and the judges rave about that. Then Seacrest interviews James, and it’s back to LiHOM James, who – before we can get our hands over our ears -- explains that, Harrison aside, he’s written his own version, with lyrics about his own struggles and that’s why he was so moved.

We’ve been expecting to see Scotty McCreery do his Elvis number ever since they started teasing us with photos of him as a baby Elvis impersonator, so it’s no surprise he’s going to do The King’s “That’s All Right.” To Scotty’s credit, he’s not doing a straight ahead impersonation and it’s pretty good. But he’s introduced a whole new set of singing tics tonight – sort of Fred Gwynne-ish -- that we have not seen before. It’s entertaining in a new way.

“I thought you were all hat and no cattle!” raves Tyler.

Pia Toscano will finally make good on her promise to get off her ballad-a-week diet and really rock it tonight, she says, with Tina Turner’s “River Deep, Mountain High.” The mentors warn her that she’s got to work it like Tina to sell this song (she’s “got to get pissed off tonight”, says I.o.vine) so we’re anticipating that she’ll do one heck of a lot more than stand here, stand there, and bend her knees a little for emphasis.

Pia makes her entrance – dressed and coifed like Gwen Stefani because, again, nothing suggests Tina Turner like …Gwen Stefani. And, right away, she walks about 10, maybe even 20 paces – and bends her knees! Then walks a circuit around the stage while singing! And her singing—it was faster!

Stefano Langone -- you surprise us. But first, Will.i.am you surprise us: in the taped bit, demonstrating how Percy Sledge really sold a song like “When A Man Loves A Woman,” we learn that you can’t sing. Actually singing, without the autotune, you sound like any guy on a street corner doing falsetto. If that isn’t inspirational to the Idolettes then we don’t know what is. Anyway, back to Stefano doing “When A Man Loves A Woman”: he’s made some kind of breakthrough, because he sounds genuine instead of his usual style, which we like to call: Look, I’m a Performer Performing a Performance! Turns out, Stefano always had a good voice, just no musical taste. Or, he wasn’t desperate enough.

Now it’s time to give it up to W.I.A., because he and Jimmy have figured out what seemed impossible: how to move Paul McDonald off the show-your-teeth-and-make-gargling-sounds performance style he’s been using all season.

Paul’s picked Johnny Cash’s “Fulsom Prison Blues” and we have grave misgivings. But, during the taped rehearsal bits, W.I.A. and Jimmy correctly point out that the crazed undertone to Cash was a major part of his appeal. “Sing it like you’re out of your [American Idol Logo] mind” urges Jimmy. And W. adds the brilliant touch of mussing up the hair like Jerry Lee Lewis. Paul gets nervous, starts to get some water. “Drink your spit!” W. snaps.

Anyway, Paul gets out on stage and it all works; the mussed hair, the reduced grinning, and a whole lot of genuine nervous energy make this performance a gas. Paul’s performance is, in addition to being his best ever in the competition, infectious. And, since the show apparently has come in short, Seacrest shows a whole lot of stage smarts and gets everybody on stage doing a hoe-down, and the band gets all cranked up, and we’re treated to a fine why-we-love-live-TV moment, in which Seacrest tries to interview the judges while they’re being drowned out. And with that, this episode of “Idol” comes to an unusually rollicking end.