Until recently, concert recordings were made in stereo, with only left and right audio channels. The advent of digital-videodisc audio technology makes richer, six-channel reproductions possible, but only for musical events originally recorded on multiple channels. Reinventing the past, Chris Kyriakakis, co-director of the Immersive Audio Lab at the University of Southern California, has found a way to revamp existing recordings by "mapping" the concert halls where they were made. Kyriakakis places arrays of microphones around the venues, then electronically compares their signals to those of reference microphones placed where the mikes were located during the original recordings. This comparison yields enough information to translate the original recording into a six-channel recording. For Internet delivery, only one or two channels need be sent; the rest are generated at playback.