Oh yeah, this is what I’m talking about:

As one participant naturally sways to the groove, the PDA’s motion sensor detects his motion and shifts the tempo of the song. With the song’s intensity building, another listener subconsciously grips her PDA tighter, introducing echo effects into the mix. The closer that listening partners move to each other, the more prominent their part in the song becomes. Meanwhile, the software applies various “error correction” techniques to prevent an onslaught of arrhythmic noise, unless of course that’s the goal. As they listen to it, the mobile music orchestra transforms the tune into a dubby, spacey version of the familiar Bjork song. […]

An artist, he says, might release a song from an upcoming album specially prepared for the Malleable Music System. Someday, malleable music may even become an art form in its own right, leading to a duet between the artist and the audience.