A tape recorder is a device that records and plays back sound using magnetism. Most tape recorders use analog technology, meaning that they create a physical representation of the original sound, as opposed to digital technology, which converts sound into a sequence of numbers. At one time analog tape recording was the definitive method for preserving sound, but today digital recording has relegated it to niche uses and boutique status.
In tape recording a microphone converts sound vibrations to electrical signals that are amplified and sent to the recorder’s recording head. The recording head is a type of electromagnet. At the same time, blank recording tape is pulled across the recording head at a carefully controlled speed by a motor-driven rotating shaft called a capstan. Recording tape is a thin plastic ribbon coated with microscopic pieces of any one of several magnetizable powders. Patterns of electromagnetism in the recording head vary with the electrical signals produced in the microphone. As a result, corresponding magnetic patterns are produced in the particle coating on the recording tape.
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 electrical signal. These electrical signals are amplified and sent to a loudspeaker or headphone, where they are converted to vibrations identical in pattern to the originally recorded sounds.
The magnetic powder most widely used in making recording media—audiotapes, videotapes, and computer hard drives—has been a type of iron oxide. Other magnetic materials used for this purpose 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.
One of the advantages of tape recording is the ability to erase and reuse tapes without the loss of recording quality. 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.
Magnetic recording dates to the 1890s, when the Danish engineer Valdemar Poulsen invented a device that stored electrical information by magnetizing particles on a steel wire. 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 were also developed. The cassette, essentially a miniature reel-to-reel mechanism in plastic or metal case, 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 phonograph records. In the late 1980s digital audio tape (DAT) recorders became available for audio recording and reproduction, but the format never won wide acceptance. In the 1990s cassettes were surpassed in popularity by the compact disc, the first major digital audio format.
