The concept behind Alvin Lucier's most famous piece, one of the landmarks of contemporary compositional music, is so simple that he explains it in a few sentences at its beginning. It's so simple, in fact, that the explanation itself is the music. Lucier notes that he's going to play the recording of his explanation back into the room, and record that, and repeat the process until the resonant frequencies of the room have eradicated the sound of his voice. Finally, he adds that the point of the exercise is "to smooth out any irregularities my speech might have."
That's the theory, but the brilliance of I Am Sitting in a Room is that its practice is much more complicated than its theory, and more moving, because of the flaws that make technology and architecture and people what they are. Most recordings don't acknowledge that they're recordings — they pretend that they're simply what you would have heard if your ears had been in some unspecified place at the right time. This one puts the lie to that idea, and makes the disparity between its setting and its listeners 'very obvious, too.
Recording and playback gear has improved over time (Lucier's first version of the piece, in 1969, lasted a bit over 15 minutes; this 1980 recording is almost three times as long), but it can't be made perfect — the space a sound is made in and the way it's recorded always affect the sound itself, and here they eventually destroy the sound. And, as becomes obvious almost immediately, the idea of "smoothing out irregularities" isn't just Zen philosophy: Lucier has a severe stutter, and eliminating his speech's irregularities means eliminating his voice altogether — you can hear him attempting to read his text without a glitch, and failing.
A few minutes into the piece, the room starts ringing audibly; phonemes fall away, little by little. For a while, the sounds that are left take the shape of the methodical, halting phrases we've heard Lucier speak over and over. Then even that melts into the air, and all that's left is wordless, hovering music, bringing the room in which it was recorded into any room in which it's heard. The map becomes the territory it describes.