Justin Bieber's 'Believe Acoustic' tops iTunes US album

Justin Bieber performs at the Jingle Ball 2012 in Atlanta, Georgia December 12, 2012. [Photo/Agencies]

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.

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"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 US 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.