* "Believe Acoustic" is Bieber's fifth studio album
* Album is instant iTunes hit
* 3 new songs, including Selena Gomez break-up ballad (Adds iTunes hit, early reviews)
By Piya Sinha-Roy
LOS ANGELES, Jan 29 (Reuters) - Justin Bieber is stripping down. Musically, that is.
The Canadian pop phenomenon showcases his vocal and song-writing talents with a new acoustic album, out on Tuesday, that also features three new tracks including a heartbreak ballad thought to be about his former girlfriend Selena Gomez.
"Believe Acoustic" sees Bieber, 18, change up the arrangements of songs from his fourth chart-topping album "Believe," released last June, singing with only a guitar or piano-driven melody.
The album went straight to the top of the iTunes U.S. album charts on Tuesday, and won generally warm reviews.
Up-tempo songs such as "Boyfriend," and "Beauty and the Beat," which roped in electronic sounds with fast-paced dance beats, are slowed down as the singer uses his vocals to manipulate the vibe of the song.
"Believe Acoustic" sees Bieber return to his acoustic roots five years after he was discovered on YouTube, singing on the streets of Canada accompanied only by a guitar.
It was released following Bieber's failure to pick up a single Grammy nomination this year, despite having a chart-topping album and a sold-out world tour.
Bieber often performs acoustic versions of his hits, most recently at the American Music Awards in November, where he delivered a stripped-down version of dance song "As Long As You Love Me."
But most ears now are turned to new track "Nothing Like Us," which follows Bieber's widely reported split from former Disney Channel star Gomez.
It features Bieber singing a raw and emotion-filled ballad over a piano melody, with lyrics such as "Girl, why would you push me away?/Lost in confusion, like an illusion ... But that is the past now, we didn't last now."
Bill Werde, editorial director of Billboard music magazine, who interviewed Bieber last week, said the song was "directly about Selena" and that fans were anticipating the singer sharing "his feelings about something this personal."
Werde said he hoped people would take notice of Bieber's song-writing and vocal production skills on the new album.
"Some of the best songwriters that are working out of our pop space are the ones that can take these very, very specific feelings that you would expect a teenager or a young adult to have and then sing and write about them in a way that makes them universal," Werde told Reuters.
"That's a skill that needs to be respected. It's not easy to write great, simple love songs."
Rolling Stone magazine gave the album three out of five stars, calling it "proof that the Bieb is, verily, a musician, whose songs work even with the high-gloss production stripped away."
Newspaper USA Today said Bieber was a "master at maximizing his material." But it added, "For people who've forgotten - or who never understood - the appeal of young performers like Bieber, 'Believe Acoustic' is a good place to hear it."
The other new songs are "I Would," a sweet love song, and "Yellow Raincoat," a mellow survival song with the singer crooning softly "cause the fame and the money and the girl will drive you crazy ... I'm thinking maybe just put on my raincoat."
If "Believe Acoustic" reaches No. 1 in the Billboard 200 album chart next week, Bieber will become the youngest artist to have five No. 1 albums under his belt. He would also be one of the few artists, including The Beatles and Jay-Z, to have a No. 1 album each year for four consecutive years.
Bieber, who surpassed Lady Gaga earlier this month to become Twitter's most-followed person, will make his television hosting debut on "Saturday Night Live" on Feb. 9, the night before the Grammy awards.
Bieber told Billboard he would not be attending the Grammy awards ceremony in Los Angeles.
Click on www.billboard.com for the full interview. (Reporting by Piya Sinha-Roy, editing by Jill Serjeant and Jackie Frank)