A method of recording electrical signals on a magnetic medium. One application is the recording of sound on magnetic tape (tape recording). In magnetic sound recording the magnetic tape is moved at a uniform speed past the poles of an electromagnet and is longitudinally magnetized. Variations in audiofrequency current supplying the electromagnet produce corresponding variations in the magnetization. During reproduction the process is reversed: the tape is fed past an electromagnet and the variations of magnetization induce currents in the coils corresponding to the original magnetizing currents. The recording medium is usually made from finely divided ferrous oxide particles and granular metallic films deposited on a plastic (cellulose acetate) tape. Multitrack tapes are available containing two or more separate recording tracks.

The electromagnet used to record, reproduce, or erase the signal on the tape is called a head (or magnetic head). It is possible to use a single read-write head to perform each separate function but commercial tape recorders usually use separate heads for recording, reproducing, and erasing. A typical head consists of soft iron pole pieces wound with wire coils. The distance between the pole pieces is the gap length and a good recorder may have a gap length as small as 0.5 allowing a sharper record and thus more faithful reproduction. The magnetic tape completes the magnetic circuit (see diagram) and the magnetization produced represents the flux pattern in the gap at the moment the tape leaves the gap. During recording magnetic bias is applied to the recording head. This is an alternating current of frequency between 60 and 100 kilohertz superimposed on the audiofrequency signal. The frequency response, distortion, and signal-to-noise ratio characteristics of the system are improved by biasing in this way. The recording is erased by causing the tape to move past the erasing head to which a large direct current is applied. This produces uniform magnetization of the magnetic material.

Magnetic tape recording

Magnetic recording of information that contains both pictures and sound is achieved using videotape. Videotape is used for storage and broadcasting. In computer systems, magnetic recording of data is made on media such as magnetic disk and specially fabricated magnetic tape (see also moving magnetic surface memory).