Instrument for reproducing sounds. A phonograph record stores a copy of sound waves as a series of undulations in a wavy groove inscribed on its rotating surface by the recording stylus. When the record is played back, another stylus (needle) responds to the undulations, and its motions are then reconverted into sound. Its invention is generally credited to Thomas Alva Edison (1877). Stereophonic systems, with two separate channels of information in a single groove, became a commercial reality in 1958. All modern phonograph systems had certain components in common: a turntable that rotated the record; a stylus that tracked a groove in the record; a pickup that converted the mechanical movements of the stylus into electrical impulses; an amplifier that intensified these electrical impulses; and a loudspeaker that converted the amplified signals back into sound. Phonographs and records were the chief means of reproducing recorded sound at home until the 1980s, when they were largely replaced by recorded cassettes (seetape recorder) and compact discs.