Those lamenting the loss of real-time action in live music, and those who celebrate the limitless wonders of sampling and computer instrumentation, ought to appreciate tape musicians. Long story short: Before tapes, there were few ways to easily record and play back sounds and music to audiences in a consistent manner. After tapes made this possible, experimental composers and musicians added them to live performances as either a substitute for a "real" instrument, or a new sound altogether. Thanks to preservationist groups like the San Francisco Tape Music Collective, the medium has avoided the fate of the dodo; the group has even started an annual festival that draws the world's most involved tape composers to perform in a dark theater surrounded by 16 speakers, helping push the art form forward. This year's headliner is surround-sound diffusion master Jonty Harrison, whose works from 1982 to 2004 will get the retrospective treatment.