LOS ANGELES (AP) — "Rock Band" is ready for an encore.

A sequel to the play-along music game that redefined the genre last year will be released first for the Xbox 360 in September, according to publisher MTV Games and developer Harmonix. "Rock Band 2" will feature a new variety of instruments, online modes and songs, and will allow players to import their previously purchased "Rock Band" tunes.

"With the original 'Rock Band,' the focus was on innovation," Harmonix co-founder and CEO Alex Rigopulos told The Associated Press. "With 'Rock Band 2,' the focus is on perfection of the experience. We've had a year to listen to our fans and build out the scope, depth and polish of the experience, so it feels like a second-generation band game."

MTV Games and Harmonix will debut "Rock Band 2" on Microsoft's Xbox 360 in September then make the game available for Sony's PlayStation 3 and PlayStation 2 as well as Nintendo's Wii later in the year. The original "Rock Band" was simultaneously released on Xbox 360 and PlayStation 3 last November before later coming to the PlayStation 2 and Wii.

"Microsoft has been a great partner for 'Rock Band,"' said Van Toffler, president of MTV Networks Music Group, which oversees the "Rock Band" franchise. "It's just so easy to download the content using the Xbox 360 system. It's evolved into a great marketing partnership as well. They'll really blow it out for us."

"Rock Band" allows up to four gamers to form a virtual band, thrashing and singing along to songs with friends online or in-person on various phony instruments. The second edition will feature a playlist of over 80 songs — all master recordings — which will include more female-fronted bands and artists who have never contributed tunes to a music game.

If you've already downloaded a song for the original "Rock Band" — at about $1.99 per track, which can't be transferred to an MP3 player — it will immediately be loaded into your "Rock Band 2" song list without needing to be repurchased or re-downloaded. It's the first time such retroactive compatibility has been introduced in a music game.

"It's the No. 1 most-requested feature from our fans," said Rigopulos.

All prior versions of "Rock Band" instruments, as well as many from the competing "Guitar Hero" franchise, will also be compatible with "Rock Band 2." Harmonix will unleash a collection of new instrument-shaped controllers, including a sturdier drum kit and a Fender Stratocaster reproduction guitar lined with faux wood-grain buttons.