Tape Recorder

Tape recordings can easily be edited by cutting out the unwanted sections and then joining the ends of the tape. However, tapes are less durable than compact discs (CD's).

This article deals with audiotape recorders, which record only sound.

Audio recording tape is a thin plastic ribbon coated on one side with particles of a substance that can be easily magnetized, such as iron oxide or chromium dioxide. A tape recorder receives sounds in the form of electric signals, which it converts into a changing magnetic field. During recording, the field places the particles on the tape into magnetic patterns. When the tape is played back, the magnetic patterns generate electric signals that the recorder uses to reproduce the original sound. Tape recording can be accomplished by two different processes. The processes are analog recording and digital recording.

In analog recording, the patterns of the electric signals are analogous (similar) to those of the magnetic signals. Analog tape recordings store a signal in a form that looks like the wave form of the original sound. In a digital recording, the electric signals are converted to a digital (numerical) code for storage on the tape. This code represents the sound. Digital recording produces better sound quality with less background noise and distortion than analog recording does. Digital technology is also used in compact discs.

In an analog tape recorder, the tape travels from the supply reel to the take-up reel past various stationary heads. Each side of the tape holds two tracks that run the length of the tape. Some digital recorders also have stationary heads. From The World Book™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. World Book diagram.

Digital audiotape can be damaged more easily than analog audiotape and so must be carefully handled and stored. Analog tape needs a thicker magnetic coating than digital tape does to store a range of electric signals. The quality of the magnetic coating, rather than its thickness, affects digital tape sound quality.

Recording tape consists of a plastic base coated with metallic particles that are easily magnetized. In recording, electric signals from a microphone create a magnetic field around a gap in the recording head. The field magnetizes the particles on the tape into a pattern like that of the sound waves entering the microphone. From The World Book™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. World Book diagram.

Before the tape reaches the capstan, it passes the heads of the tape recorder. The heads are small electromagnets that erase, record, and play back. The speed at which the tape moves past the heads depends on the type of tape recorder. The speeds are measured in inches per second (ips). The most commonly used speeds are 17/8, 33/4, 71/2, and 15 ips (4.8, 9.5, 19, and 38 centimeters per second). The higher speeds produce recordings of the best quality, but recording at slower speeds adds to the playing time of the tape.

Erasing and recording. When an analog tape recording is made, the tape first comes into contact with the erase head. The erase head, which is automatically activated during recording, produces a strong magnetic field that removes any previous recording from the tape. The blank tape then moves past the recording head.

The sounds to be recorded on the tape are translated into a varying electric current by a microphone. An amplifier strengthens the current, which is then fed into the recording head. As the current flows through the head, it sets up a changing magnetic field around a small gap in the electromagnet. When the analog tape passes the gap, the magnetic field places the magnetic particles on the tape into a pattern that represents the sound waves entering the microphone.

Unlike analog recorders, most digital recorders have no erase head. Instead of erasing the tape first, they use a process called overwriting to record new sound. Recording and playback heads may be either stationary or rotating. Stationary heads are like the heads on an analog tape recorder. In a rotating system, two heads are mounted opposite one another on a rotating cylinder called a drum. During recording and playback, the tape moves past the spinning drum.

A digital audiotape recorder converts the original electric signals to digital information in several steps. First, the signal is filtered to prevent interference from unwanted high frequencies. Next, each second of sound is broken up into thousands of segments called samples. Each sample is given a numerical code, which is recorded on the tape in the form of magnetic patterns.

Different kinds of tape recorders use different widths of magnetic tape. Most tape recorders can record more than one track (separate recording) on a tape. To produce stereophonic sound, a tape recorder must be able to record at least two tracks at the same time, each track from a different channel.

Playing back. Before a tape recording can be played, it must be rewound on the supply reel. The tape is then sent through the recorder again. This time, the playback head is switched on, and neither the erase head nor the recording head is activated. As the tape passes the playback head, the magnetic patterns on the tape generate a weak electric current in the electromagnet. An amplifier strengthens the current before it reaches a speaker, which reproduces the recorded sound.

During playback, the pattern of the current generated by an analog tape corresponds to the pattern of the recorded sound waves. Playing a digital tape produces electric pulses that represent a numerical code. The recorder translates the code into a varying current, which an amplifier strengthens and sends to the speakers.

Open-reel tape recorders are used by recording studios and broadcasting stations. They produce better-quality sound than do cassette recorders. To use an open-reel recorder, the operator places a supply reel and a take-up reel on spindles on the outside of the recorder. The tape is threaded by hand past the heads of the recorder and through the capstan and pinch roller.

Recording studios usually record at 15 ips or 30 ips (38 or 76 centimeters per second). Many professional analog recorders use 2-inch (5-centimeter) tape, which carries 24 tracks. Professional digital recorders often use 1/2-inch (1.3-centimeter) tape, which carries up to 48 tracks. Such analog and digital recorders are called multitrack tape recorders.

Cassette tape recorders are widely used in homes and automobiles. Portable cassette recorders are also popular. Cassette recorders are easier to operate than open-reel recorders because the tape does not have to be threaded through them. A cassette recorder uses a small plastic case, called a cassette, which encloses a miniature supply reel and take-up reel. The cassette is snapped into the recorder.

A cassette deck, also called a tape deck, is a recorder and player. A deck usually operates as a component (part) of a stereophonic sound system and is connected to an amplifier and speakers. Decks typically have electronic noise reduction systems, which reduce the faint hissing sound made by the tape. Features called synchronized start and dubbing allow recordings to be made from compact discs or from cassette tapes. An auto reverse feature switches the direction of tape movement so that the other side of the tape plays back.

Cassette tape measures only 0.15 inch (3.81 millimeters) wide. Analog cassette tape carriers four tracks, two on each side. Analog cassette tape operates at 1 7/8 ips (4.8 centimeters per second).

Digital formats for cassettes include (1) the DAT (digital audiotape) cassette and (2) the digital compact cassette (DCC). Each type requires a special player.

DAT cassettes produce far better sound quality than do analog cassettes. A DAT cassette is smaller than an analog cassette but has a longer playing time. It uses two tracks and is played on only one side. A DAT cassette operates at 0.321 ips (8.15 millimeters per second), using a rotating head.

A DCC is the same size as an analog cassette and operates at the same speed. It has nine tracks and is played on only one side. DCC's produce sound of nearly the same quality as DAT cassettes. In DCC recording, sounds that cannot be heard by the human ear are sifted out electronically. This sifting reduces the audio information stored on tape. A DCC recorder can play back analog cassettes.

A small number of audio recorders began to be produced commercially in the early 1930's. Initially, steel wire and steel ribbon were the only recording materials used. But they were awkward to handle and store and nearly impossible to edit. During World War II (1939-1945), German engineers perfected the magnetophon, the first recorder to use plastic magnetic tape.

By 1950, tape recorders were being widely used in the radio and recording industries. Manufacturers began to produce stereo tape recorders for use in the home in the mid-1950's. Cartridge tape systems were introduced in 1958. Such systems, which are often called 8-track, used an endless loop of tape in a cartridge to play four stereo music programs. Eight-track systems were especially popular for playing musical recordings in automobiles.

In the mid-1960's, cassettes revolutionized the tape recorder market. They gained even greater popularity when noise reduction was added, and they began to compete with phonograph records.

Manufacturers introduced digital recording systems in the 1970's. The market for prerecorded music in the United States became even more competitive in 1983 with the introduction of audio compact discs. By the 1990's, CD's had largely replaced phonograph records, but audiotapes remained popular. Digital audiotape recorders became available in the 1990's.

Since 1992, manufacturers of blank digital tapes have been required by law to pay royalties (shares of profit) into a fund, for distribution to recording companies, music publishers, and song writers. Consumers are permitted to use the blank tapes to make copies of recordings for their personal use only. Selling such copies is illegal.

Contributor: Ken C. Pohlmann, M.S.E.E., Prof. of Music Engineering, Univ. of Miami.

See also Electromagnet; Phonograph; Speaker; Stereophonic Sound System.

Rumsey, Francis, and McCormick, Tim. Sound and Recording. Focal Pr., 1992. Chapter 8 discusses tape recording

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