The foundation of this piece, and much of
Steve Reich's, is what is known as
phasing, what
mattbadass describes as the pedal tone of
octave C's.
In Reich's music, like Music for 18 Musicians, which is founded on this work of Riley, the attempt is made to play the notes together, but that is never quite realized. Listening to them, they phase in and out, coming on the beat, they slightly before and after it.
This creates an hypnotic foundation for the other instruments, and voices.
The recording of In C I heard, used multiple recording techniques to add additional layers to the performance.
Far from being absurd, in my experience with Riley's, and Reich's work, and those influenced by them, I found it quite ecstatic, in the fundamental sense of taking one out of one's body.
And that just happens to be Reich's stated goal in his Words About Music. Unlike the aesthetic distance (see Why Play Bach?)
and actual distance in conventional music, but a complete elimination of all barriers in joy.