I've read about it in 2 or 3 different places, the most recent being in the last issue of TapeOp. I think that it was in an issue of EQ or Recording last year, as well. The mics were gated, so that the quiet passages were only in the close mic, the louder passages turned on the second mic, and the loudest passages activated the third mic. Instant volume-dependant reverb!
-mg