When psychedelic bands of the late 1960s began to experiment with stereo separation, they were rediscovering a technology invented by AT&T more than 30 years earlier. Stereo grew out of AT&T's attempts to reduce harmonic distortion in phonograph records. AT&T engineers substituted vertical groove cutting for the old, wider, side-to-side method, and got better stylus tracking and hi-fidelity. Then they decided to try two-channel recording -- and stereo was born.

  AT&T demonstrated its early prowess with stereo by placing microphones in concert halls to broadcast stereo symphonic music over giant loudspeakers. AT&T also conducted research into the science of sound direction by making volunteers wear a fake human head while sitting in a huge, sound-absorbant room.