Tape recorders capture, store and play back audio on a magnetic medium.Originally, tape recorders were bulky machines that required two large reels of tape. Today, most recorders use compact cassette tapes to store the sound.

The development of tape recorders transformed the radio and television industries, making it possible to prepare a show ahead of time instead of broadcasting it live.

Function
Tape recorders are based on the same principles as the magnetic wire recorders of the 1800s. A magnetizable wire or tape rolls past the recording head at a continuous rate of speed. The recording head receives an electrical signal that corresponds to the sound being recorded. As the tape moves past the head,it is magnetized in a pattern that represents the electrical signal. When the tape is played, the playback head reads the magnetized pattern and converts it back to an electrical signal.
Steel Tape Recorders
The first tape recorders used a steel tape instead of a wire. The earliest steel tape recorder, called the Blatterphone, was developed in 1929 by the Ludwig Blattner Picture Corp. In 1932, a Marconi-Stille steel tape recorder was used by the British Broadcasting Co. for its first prerecorded radio broadcast. Steel tape recorders had several disadvantages that limited their popularity. The audio quality was poor, the reels of tape were cumbersome and heavy, and the steel tape itself was dangerously sharp and could cause injury if it broke and came off the reels at high speed.

American Innovations
After World War II, American engineers had several seized German tape recorders to study and improve upon. In 1948, Ampex introduced its Model 200 tape recorder, which revolutionized the entertainment industry. It was used to produce the first tape-delayed radio broadcast in the United States. While Ampex was developing its tape recorders, Minnesota Mining and Manufacturing was hard at work creating a reliable magnetic tape. American entertainer Bing Crosby was instrumental in helping Ampex dominate the tape recording market.He was so impressed with the potential of magnetic tape recorders that he invested $50,000 in the company.

Cassette Tape Recorders
In 1963, Philips introduced the compact cassette, and the popularity of tape recorders skyrocketed. The company chose to license its cassette format to other companies at no charge, making it the primary medium for audio recording around the world. It quickly became a convenient method of selling prerecorded music, outlasting the vinyl LP and surviving into the era of the compact disc.Portable cassette tape recorders like the Sony Walkman made it possible to listen to and record audio almost anywhere.

German Innovations
The German companies BASF and AEG worked together to develop the first modern magnetic tape recorder in the 1930s. Instead of a sharp, pointed recording head, the German recorder used a ring-shaped head that did not damage the tape as it passed by. The Germans also developed the technique of AC biasing to improve sound quality. In AC biasing, a high-frequency signal is added to the audio being recorded. This signal pushes the frequency into the magnetic tape's optimum range when the tape is played back.

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