Although I sometimes say nice things about music games such as Guitar Hero, I don’t host enough parties to justify spending money on them, but I might consider buying a fake plastic guitar for Instant Jam, a music game that launches in closed beta on Facebook today.

At a glance, Instant Jam looks like Guitar Hero for the PC. Colored notes scroll down the screen, prompting you to press keyboard buttons in step with the guitar track. You can also use guitar controllers from other games, as long as they have USB output.

Here’s the big twist: Instant Jam uses music you already own, reading songs off your hard drive and matching them with a database of note charts. If a note chart exists for your favorite tune, you can play it in Instant Jam for free, and if a chart exists for a song you don’t own, the game provides links to iTunes and Amazon. Furthermore, there’s no music licensing involved, so even artists that have refused to appear in Guitar Hero and Rock Band, such as Led Zeppelin, are represented among the initial 2,000 songs.

Instant Jam’s executive producer, Amir Rahimi, assures me that bypassing music labels and musicians is completely legal, because the game is merely playing back your music library with an interactive layer on top. Along these lines, you might notice a couple differences from Guitar Hero or Rock Band. For instance, when you flub a note, the overall volume decreases and a garbled sound effect plays, but the guitar itself is never muted. That’s because Instant Jam uses final recordings instead of master tracks. You also won’t see on-stage avatars playing along. (Rahimi says avatars could be added later, but I’m guessing they won’t be able to mouth specific lyrics or do anything that could be interpreted as a derivative work.)

Unlike Guitar Hero and Rock Band, Instant Jam has no single-player campaign and no live multiplayer. The game’s main thrust is social networking, encouraging players to challenge each other remotely for high scores and level up by earning “fans.” Doing so unlocks currency, which can be spent on new visual effects. It should be a familiar formula for anyone who’s played social games like Mafia Wars, but compared to the living room parties of console music games, it makes for a decidedly solitary experience, for better or worse.

Instant Jam is free to play on Windows PCs, with Mac support coming soon, but the number of songs you’re allowed to play in one sitting is limited. There are plenty of opportunities to earn more free plays — simply looking at friends’ profiles earns fans, which can unlock more plays, and challenges are always free — but eventually you’ll hit a wall, at which point you can pay for more plays (in-game currency comes in $5 increments, and each play costs roughly a penny) or wait an hour and a half for plays to recharge. Instant Jam will also make money by selling virtual goods, including special guitar necks and bodies, and by collecting affiliate revenue from music sales.

To promote Instant Jam, developer InstantAction will use embedding technology that allows the game to be published on any web page like a YouTube clip. Embedding was supposed to be ready today, but the game’s being limited to Facebook while developers squash bugs.

I did a little late-night jamming in a private beta after getting home from the bar on Saturday. (Isn’t that the only way to play music games?) Clearly there are some bugs that need fixing — sometimes the song entered an endless loop after the performance was over, other times the music fell out of sync with the note chart, and the game failed to recognize all the songs in my library, forcing me to browse the entire Instant Jam catalog for matches and load songs manually.

But my biggest gripe is with the note charts themselves. Some songs are dead-on, but developers got lazy with a few of the guitar solos, even iconic ones like the jam from Pink Floyd’s “Money” (the notes were not even close to what was being played) and the solo in Soundgarden’s “Black Hole Sun.” (You play the rhythm guitar track instead. Seriously?) Rahimi said Instant Jam may crowdsource note charts in the future. This will have to happen if in-house transcribers can’t pay more attention to accuracy.

Drawbacks aside, I’m still excited about Instant Jam, if only because it tosses out the double-dipping in which every other music game indulges. Being able to buy a song once and enjoy it in many ways? That’s worth paying for.

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