I Am Sitting in a Room

Wiki:

I Am Sitting in a Room (1970) is one of composer Alvin Lucier's best known works, featuring Lucier recording himself narrating a text, and then playing the recording back into the room, re-recording it. The new recording is then played back and re-recorded, and this process is repeated. Since all rooms have characteristic resonance or formant frequencies (e.g. different between a large hall and a small room), the effect is that certain frequencies are emphasized as they resonate in the room, until eventually the words become unintelligible, replaced by the pure resonant harmonies and tones of the room itself. The recited text describes this process in action—it begins "I am sitting in a room, different from the one you are in now. I am recording the sound of my speaking voice," and the rationale, concluding, "I regard this activity not so much as a demonstration of a physical fact, but more as a way to smooth out any irregularities my speech might have," referring to his own stuttering.

Lucier had also specified that a performance need not use his text and the performance may be recorded in any room. However, Lucier himself has recorded the piece in at least one room he did not find aesthetically acceptable.

"I am sitting in a room different from the one you are in now. I am recording the sound of my speaking voice and I am going to play it back into the room again and again until the resonant frequencies of the room reinforce themselves so that any semblance of my speech, with perhaps the exception of rhythm, is destroyed. What you will hear, then, are the natural resonant frequencies of the room articulated by speech. I regard this activity not so much as a demonstration of a physical fact, but more as a way to smooth out any irregularities my speech might have."