After receiving a letter accusing them of patent infringement, Activision filed a declaratory judgment action March 12, 2008, against Gibson Guitars, asking the court for finding of invalidity and noninfringement. Gibson is asserting that it has a patent on a musical performance simulation, which Gibson alleges Activision infringes via its popular Guitar Hero games.

The lawsuit was filed in the Central District of California. The patent is U.S. Pat. No. 5,990,405, entitled "System and Method for Generating and Controlling a Simulated Musical Concert Experience," issued Nov. 23, 1999. At a glance, the broadest claim appears to be:

13. A system for simulating participation of a user playing a musical instrument in a pre-recorded musical performance having audio and video portions, the musical instrument producing instrument audio signals at an instrument audio output when the instrument is played, comprising:

a. a source playback device for playback of the audio and video portions of the pre-recorded musical performance through corresponding source audio and source video outputs;

b. a source audio control device for controlling one or more characteristics of the audio portion of the pre-recorded musical performance during playback, the source audio control means operably connected to the source audio output and to the instrument audio output and having a controlled audio output; and

c. the source audio control device is responsive to the instrument audio signals whereby at least one characteristic of the audio portion of the pre-recorded musical performance is controlled by playing of the musical instrument by the user.

We'll keep tracking this case and let you know of any major developments.