"Do you realize the sound only comes from one person? I've got a way to make it follow the person."
Alan Blumlein, electrical engineer
For most people, "stereophonic" means listening to audio through a two-channel loudspeaker system. Different elements of the recording can be heard to come from different directions, just as the human ear is naturally able to pinpoint the location of a sound.
The man who invented stereophonic sound was an English electrical engineer named Alan Blumlein (1903-1942). While watching one of the early "talkies" in his local cinema in 1931, he became distracted by the disembodied effect of voices coming from a single location when the actors speaking were positioned across the cinema screen. The system he developed to enable the sound to "follow" the voice was called "binaural"—what we now know as stereo. His idea was a simple one. Two microphones were set apart by a fixed distance, each microphone connected to an audio channel. The position of the actors' voices would then be positioned in the binaural "spectrum" according to how much volume each voice projected to each channel. If the recording was replayed over a two-channel system—with one loudspeaker placed on either edge of the screen—the voices would indeed reflect the position of the actors on the screen,
Blumlein filed a series of related patents at the end of 1931, including not only his binaural system, but a method in which two channels could be captured in the single groove of a gramophone record.
