Process Of Electricrecordings

process of converting the acoustic energy of sound into some form in which it can be permanently stored and reproduced at any time. In 1855 the inventor Leon Scott constructed a device called a phonautograph that recorded tracings of the vibrations of sound. Thomas Edison, starting about 1877, made great improvements in mechanical sound recording and was the first inventor to achieve the actually audible reproduction of recorded sound. The greatest advances, however, were made after the adoption in 1925 of electromechanical systems using electronic amplifiers (see record player ).

Generally, in recording, the sound waves impinge on a microphone and are converted into an electrical signal that is recorded by a tape recorder. The tape can be edited if desired. When a commercial phonograph record is to be made, a disk of soft acetate composition coated on an aluminum base, called an original, is placed on a rotating turntable. The tape is played back and controls a stylus that cuts a spiral groove starting from the outer edge and moving to the inner edge of the original. For monophonic sound the stylus vibrates from side to side as it cuts the groove. For stereophonic sound the stylus vibrates vertically, as well as from side to side, recording one sound channel in the left wall of the groove and one in the right.

In a series of steps the original is used to make a metal stamper that presses the groove into commercial records. In order to play a commercial record, a stylus, or needle, is placed in the disk's groove while it is in motion on a turntable. The vibrations of the stylus cause the transducer to which it is attached to produce a varying voltage. This voltage is amplified and fed into a loudspeaker.

In magnetic tape systems the varying electrical voltage is converted in a small electromagnet, called a head, into a varying magnetic field that causes magnetic particles embedded in the tape to become aligned in varying degrees as the tape passes through the magnetic field. On playback, the magnetic tape moves past the head, generating a varying voltage in the coil of the head, which is boosted