On TV: Christina Aguilera changed how TV music shows are judged

NBC announced Monday that Shakira and Usher will join "The Voice" as judges in the spring, filling in for Christina Aguilera and Cee Lo Green as those two embark on other projects -- Aguilera is releasing a new album and touring while Green is working on new music and developing a scripted comedy series based on his life. But years from now, Aguilera likely will be remembered as the person who almost single-handedly reshaped music-competition reality programming. Her legacy as a judge on "The Voice" may well turn out to be deeper and more profound than the one she's forged in her music career.

Securing Aguilera in 2011 was a coup for a show that needed to differentiate itself from Fox's "American Idol," which had just signed Steven Tyler and Jennifer Lopez as judges.

But for all their fame, Tyler and Lopez were past their fertile period as hitmakers. Aguilera, though not quite in her prime, had been in the Billboard Top 10 as recently as 2008. Of the four mentor-judges of "The Voice," she was the one most obviously slumming it on this television gig, even though she was coming off a bumpy professional period: a flop album, "Bionic"; an awkward and sloppy rendition of the national anthem at the 2011 Super Bowl; and an arrest on a charge of public intoxication.

But Aguilera was an undeniable contemporary pop star, and her presence elevated those around her: Blake Shelton, a country star largely unknown outside that world; Adam Levine, the frontman of a popular

but ineffectual band, Maroon 5; and Cee Lo Green, accidentally, and briefly, a pop star as part of Gnarls Barkley.

Broadly speaking, it's because of Aguilera that on Sunday, after weeks of speculation, it was announced that Nicki Minaj and Keith Urban, contemporary hitmakers both, would become part of the "Idol" judge panel. (They effectively replace Tyler and Lopez.) They join Mariah Carey, who signed on in July and is now the panel's unlikely eminence grise, and Randy Jackson, the lone holdover from "Idol" 1.0.

! Aguilera's shadow also extends over "The X Factor," the Fox competition that last week gave its new judge-mentor panel its debut: The two older male executives, L.A. Reid and Simon Cowell, remain from Season 1, but the two women, Paula Abdul and Nicole Scherzinger, have been replaced by more current names: the former Disney star Demi Lovato and the former Aguilera nemesis Britney Spears. Spears had a No. 1 album last year, and Lovato has had two Top 20 singles in the last 14 months.

It is no longer a choice between music star and television star. In fact, to be modern, it's best to be a little of both. Aguilera, Spears, Minaj and Lovato are all more or less current pop stars. On a smaller scale, the same goes for Urban, Shelton, Green and Levine. Carey, while older and more experienced, is certainly still an active pop threat.

As a group, they're using these shows not as a platform for stalled-career kick-starting, but as part of a portfolio of activities to remain relevant in the industry.

worst day _ is an extremely dangerous and powerful delivery platform, and one that must look even more attractive as the music industry struggles to sustain its thinning revenue streams.