Sound Recording

sound recording, 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 in an amplifier and converted to sound by a loudspeaker.

Compact discs, first introduced commercially in the early 1980s, employ laser technology to inscribe and "read" digital information in a way that avoids actual physical contact between the disc and any type of stylus. The optical properties of the disc's tracks are measured by a sensor and converted to digital signals and then to sound. Compact discs have the advantage of minimal wear and a greater possible dynamic range. Compact disc technology was superceded by digital versatile disc (DVD) technology with the introduction of the DVD-Audio format in 1999. Using a similar optical technology, DVD offers greater storage capacity and even more accurate sound reproduction. Recorded music and other sound may also be stored on and played from computer disks using several different computer-program file formats.

Motion picture soundtracks are called optical recordings. The sound to be recorded is converted into an electrical signal that is used to modulate the intensity of a beam of light. This modulated beam exposes a moving film to make a recording of the sound. Reproduction is effected by shining a steady beam of light through the developed film that is the sound track. As the film moves across the light beam, some of the light passes through it into a photocell, the amplified output of which activates a loudspeaker. See tape recorder.

Bibliography

See L. Baert et al., Digital Audio and Compact Disc Technology (1995); F. Jorgenson, The Complete Handbook of Magnetic Recording (1995); J. Borwick, ed., Sound Recording Practice (4th ed. 1996); G. Alkin, Sound Recording and Reproduction (3d ed. 1997); R. E. Runstern and D. M. Huber, Modern Recording Techniques (4th ed. 1997); B. Bartlett and J. Bartlett, Practical Recording Techniques (2d ed. 1998).

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sound recording [′sau̇nd ri‚kȯrd·iŋ]

(engineering acoustics)

The process of recording sound signals so they may be reproduced at any subsequent time, as on a phonograph disk, motion picture sound track, or magnetic tape.

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Sound Recording 

the process of recording acoustic data for storage and subsequent reproduction; the recorded data are also called a sound recording.

Sound recording is based on changes in the physical condition or form of various portions of the recording medium, which may be magnetic tape, a phonograph disk, or motion-picture film. Sound recording is a particular case of the recording and reproduction of information (data storage and retrieval) and is accomplished by two methods, acoustic and electroacoustic. In the first method, the sound vibrations directly actuate a device that acts on the recording medium; in the second, the vibrations are initially converted by a micro-phone into electrical oscillations, whose power is increased by an amplifier to the required value, whereupon they are fed to a device that acts on the medium—that is, the sound is recorded indirectly. The electroacoustic method provides better recording quality and greater possibilities for use; it has almost entirely superseded the acoustic method. Electro-acoustic methods, in which the electrical oscillations initially produced from the recording track are amplified and converted into acoustic oscillations by a loudspeaker, are usually used in the reproduction of recordings. Three main systems of sound recording—mechanical, photographic, and magnetic—are in practical use.

In mechanical recording a needle or stylus impresses or cuts a groove in the surface of the moving recording medium; the shape of the groove corresponds to the form of the re-corded acoustic vibrations. During the process of reproduction by an electric phonograph, the needle repeats the vibrations as it moves along the groove and transmits them to a diaphragm, which radiates the sound through a horn, or to an electromechanical transducer in the phonograph pickup, which produces electrical signals. The first practical mechanical sound recording was made in 1877 by the American inventor T. A. Edison, who built a phonograph that recorded the sound on a roller wrapped in tinfoil. The foil was subsequently replaced by wax. Mechanical sound recording on phonograph disks has become very popular because of its simplicity and convenience for the reproduction of sound in the home.

In photographic recording, the intensity or shape of a light beam that falls on a moving motion-picture film is varied (modulated) by the sound vibrations. As a result, the sound is “photographed.” After chemical development a darkened sound track, which varies either in transparency or width according to the recorded vibration, is formed on the film. To reproduce the sound, the film is moved at the same speed as during recording, and the photographic sound track is illuminated by a light beam that passes through it to a photocell. The photocell converts the variations in light intensity into electrical oscillations. The prototype of photographic sound recording apparatus was the photophone, which was invented by the German engineer E. Ruhmer in 1901. Photographic sound recording is used mainly for sound motion pictures.

In magnetic recording, individual parts of a medium moving through a magnetic field are magnetized according to the acoustic vibrations. The field is created by a magnetic head with a winding through which the amplified microphone currents are passed. During reproduction the reverse conversion takes place: the moving magnetic sound recording excites electrical signals in the head. The first apparatus for recording sound on steel wire (the “telegraphone”) was proposed by the Danish engineer V. Poulsen in 1898. Magnetic sound recording on tape by means of tape recorders, which are the simplest and most convenient type of equipment for home use, became widespread in the 1940’s.

Sound recording is developing in terms of improvement of the three systems listed above and a gradual shift from monophonic to stereophonic recording, in which the listener receives information on the spatial location of individual sound sources: the sound assumes a “spatial quality,” so that in many respects its reproduction becomes more natural.

V. G. KOROL’KOV

Sound recording in radio broadcasting. During the 1920’s the use of sound recording in programs was sporadic, since the very process of recording was not a component part of the broadcasting industry. The introduction of magnetic sound recording in the early 1940’s as a part of the process of preparation of radio programs was a revolutionary factor in the development of radio broadcasting; it provided the prerequi-sites for the emergence of new expressive means, as well as qualitatively new forms and genres of broadcasting. The recording and transmission of public events became routine. Sound recording made possible the development of radio journalism, radio dramas, radio theaters, and music broad-casts and the preservation and use of examples of dramatic art, expertise of performance, and the people’s art as a permanent stock.

Sound recordings are classified according to their content. Documentary recordings include records of events, speeches, and interviews. Documentary-artistic recordings are usually compositions that combine documentary, journalistic, and artistic recordings. Artistic recordings are recordings of the literary, theatrical, and musical arts, as well as of original productions for radio (such as radio plays). Sound-effects recordings are used extensively to create an aural background that helps both the performers and the listeners to experience the actual environment and activities (the illusion of presence).

Sound recordings are also classified according to such criteria as the place and method (studio, remote, and relayed recordings), the storage time and duration of broadcast use (stock, including one-time, and unique recordings), and the intended purpose (educational, scientific-educational, artistic-educational, entertainment, advertising, and so on).

Stock sound recordings are intended for long-term preservation and repeated use in broadcasts. As a rule, they are recordings of historical events, speeches by statesmen and public figures, outstanding literary, musical, and theatrical compositions performed by famous masters of the arts, and folklore. Stock recordings are distinguished by their high technical level and, wherever possible, are made in special studios, where several versions are made, the best of which is edited for use in stock. Since the 1960’s most of the stock recordings of the All-Union Radio and the All-Union Recording Studio have been made in the compatible stereo mode, which is also suitable for monophonic reproduction.

One-time recordings are produced to eliminate performance errors and accidents that may occur during a live transmission, as well as for use when the performers are not in the studio. They are usually erased after being broadcast. About 75 percent of the broadcasts of the All-Union Radio are recorded in advance so that they can be included in broadcasting programs for the different time zones of the various areas in the USSR and other countries.

Sound recording in education. Sound recording (disk records) was first used for educational purposes in the early 20th century in the USA and some European countries, including Russia. The first educational recordings were produced especially for schools in the USSR in 1936 (disk records for foreign-language lessons). In the 1950’s mass production of educational sound texts for general-educational schools and other types of educational institutions was begun. The principal types of educational sound recording texts are sound supplements to foreign-language textbooks for general-educational schools and institutions of higher learning, as well as self-instruction manuals for the independent study of foreign languages; recorded collections of literature, history of the USSR, and musical literature; sound filmstrips on language and literature; recordings of lessons by famous music teachers, discussions about music, self-instruction manuals for musical instruments, and musical dictations; scientific-educational and artistic-educational lectures by well-known figures in science, technology, and culture; tours to memorable places and museums; calisthenics lessons; and recordings of the aural symptoms of various illnesses. The texts are usually recorded on phonograph disks. In the 1960’s, sound-recording technology and language laboratories became common in institutions of higher learning and secondary specialized educational institutions (especially for the humanities). Magnetic recording is used primarily to master living conversational speech in the study of foreign languages and for improving the quality and delivery of one’s own speech (in musical and theatrical educational institutions). In this respect, magnetic recording is a unique means of self-monitoring, since it makes possible the analysis of the sound of one’s own speech and delivery.

I. P. VEPRINTSEV, E. O. KONOKOTIN, and V. N. RUZHNIKOV

REFERENCES

Apollonova, L. P., and N. D. Shumova. Mekhanicheskaia zvukozapis’. Moscow-Leningrad, 1964.
Parfent’ev, A. I., and L. A. Pusset. Fizicheskie osnovy magnitnoi zapisi zvuka. Moscow, 1957.