Today, Harmonix announced the details about a major patch for the Xbox 360 and PS3 versions of “Rock Band” that includes a new in-game music store. The update will be available this week for both platforms, according to the developer.

The Cambridge-based studio, which is owned by MTV Networks, also revealed today that six million songs have been downloaded since the game’s November 20 launch.

MTV Multiplayer was able to see a demo of the store’s features earlier this month in New York. The new music store is accessible through the main menu listed after the “Community” tab, and the purchasable songs are categorized by new releases, song titles, song packs and albums. Albums are not available yet, but are indicated to be “coming soon.” You can also sort the downloadable tracks by artist name, genre, difficulty and year.

New tunes will be marked with “New!” and the store will recognize if you’ve already downloaded a song by marking it as “Sold” to prevent you from accidentally acquiring the same song twice. Within the store, aside from pricing, you’ll also be able to preview the songs and see the album artwork.

Another addition to the music shopping experience is the denotation of difficulty for each track; on a nine-point scale, players can see a song’s difficulty for each instrument as well as the band as a whole. I wondered why they chose a nine-point scale. “When I asked ‘Why not out of ten?’ [The developers] were like, ‘Because it’s out of nine,” Harmonix rep John Drake told me at the demo, laughing. When I asked if the handy new difficulty ratings would be retroactively applied to the on-disc tunes, he said, “That’s something we’re looking into, but it’s not planned at the moment.”

The music store patch also includes several fixes to the game. Read on to see the revisions as well as screenshots of the new music store.

- Adjusted fan caps for “Band World Tour” mode: For those playing on Easy, Medium or Hard, they’ll be able to earn more fans, therefore allowing bands to get further along on the tour. Easy players will be able to cross the Atlantic, Medium players can get access to more venues, and Hard players on the Xbox 360 can unlock the “One Million Fans” Achievement.

- Better randomization on the randomized setlists: If you’ve noticed Weezer’s “Say It Ain’t So” and certain Metallica tunes showing up more frequently than others on the “random” setlists, Harmonix has too. “You’ll be glad to know that we’ve tracked down and fixed the issues that triggered these very repetitive moments in Band World Tour,” Senior Designer Dan Teasdale wrote on the “Rock Band” forums.

- Improved detection and scoring for phoneme recognition: Teasdale wrote, “If you had trouble [singing] on songs like ‘Timmy and the Lords of the Underworld’ and ‘Blitzkrieg Bop,’ you should have an easier time beating these songs now.”

- Faster loading of downloadable content: DLC loads faster, and the information is now cached so that the load time wait occurs only once, versus every time the game is turned on. “The reason [DLC took so long to load] is because we have to cache all of those audio sample onto your hard drive,” Drake explained at the demo. The new music store will only have audio for the songs you choose to preview, versus automatically previewing every track on the list when you scroll over it like in the in-game setlists.

- Microphone latency on PS3 is “improved”: According to Teasdale’s forum post, microphone latency in “certain situations” has been reduced. At the demo, Drake had explained that high-end AV set-ups had mic and drum fill lag issues that affected a small but vocal amount of users. “It should now be synced up as humanly possible,” he added.

- Xbox 360 band logos visible on Xbox Live: Parental controls previously stopped band logos from being visible on Xbox Live.

For those who have more questions and comments about the game (and we know there are many of you), Teasdale had this to say at the conclusion of his forum post:

“…we’re very aware that there are features that the community has requested that aren’t addressed in this software update. I want to make it very clear that we’re listening to all of your requests, and actively want to get these features onto the Rock Band platform in the future — but when we do add them, we also want them to be 100% perfect, and not rushed just to make it into any specific software update.”