A variety of machines have been devised to record and play back sound. Among them are open-reel recorders, cassette players, and microcassette players. Once popular, the eight-track cartridge player has largely fallen out of use. One of the advantages of these players is their ability to erase and reuse tapes without the loss of recording quality. Practically any information that can be converted to an electrical signal can be stored on a magnetic tape with the help of a tape recorder. - Electronic impulses fed into the tape recorder are converted into magnetized patterns that are …
This process is reversed in playback. The recording tape bearing magnetic patterns is mechanically pulled across the playback head, which is also an electromagnet. The magnetic patterns stored on the tape produce corresponding electromagnetic patterns in the head that are converted to an electric impulse. These electrical impulses are amplified and sent to a loudspeaker or headphone where the electric signals are converted to vibrations identical in pattern to the originally recorded sounds (see Electricity). The magnetic powder most widely used in making recording media—audio tapes, videotapes, and computer data storage tapes and disks—has been a type of iron oxide. Other magnetic materials used in recent years include chromium dioxide, nonoxide iron, and a cobalt-absorbed ferric oxide particle. Each magnetic material offers slightly different advantages in the areas of frequency response at one or both ends of the sound spectrum, signal-to-noise ratio, and useful recording tape life. (See also Video Recording.) Modern recording tapes consist of a plastic-based film coated with one of the magnetizable powders that is held in place by a binder. Mylar and other polyester plastics are widely used as the tape base. This base is often back-coated with material designed to eliminate static electricity buildup. The binder is a type of glue that can be applied evenly to the plastic base while bonding the magnetic particles to the base. The binder must hold the magnetic particles apart from each other, yet remain flexible when dry. It must not stick to itself when the finished tape is wound and stored. Through an electromagnetic erase head, a recorded signal can be removed, and the tape can be reused. If the recording tape breaks, it can be spliced and repaired. A section of damaged recording tape can be physically cut out. If the remaining ends are spliced together, the tape can still be used. The rate at which the magnetic tape travels past the recording and playback heads is controlled by the recorder's drive mechanism. The most common drive mechanism in tape recorders is the capstan drive. In a capstan drive system, the magnetic tape is trapped between a cylindrical piece of rubber called a pinch roller and a motor-driven cylinder called the capstan. The rotational speed and diameter of the capstan determine the speed of the tape. Valdemar Poulsen, a Danish engineer, patented a magnetic wire recorder in 1898. The tape recorder was essentially developed into its modern form in Germany in the 1930s and 1940s. After World War II, experimenters in the United States quickly improved on the design and operation of German equipment. The tape recording of radio programs for later broadcast began in the late 1940s. Beginning in the 1950s, reel-to-reel (also known as open-reel) stereo tape recorders became available for home use. Other tape formats that operate at fixed, generally slower, speeds have also been developed. The cassette, essentially a miniature reel-to-reel mechanism in an enclosure, was introduced in 1964. By the 1970s cassettes had become capable of high-fidelity and by the early 1980s the sales of music cassettes exceeded those of standard phonograph records. For portable use, cassette players may be battery powered and contain built-in microphones. |