Hard magnetic material is magnetized, but also left over remanence, the strength and direction of remanence with the magnetization of magnetic strength and direction may be. Tape is composed of tape base, adhesive and magnetic layer. Band base is generally made of polycarbonate or vinyl chloride. Magnetic powder is the residual magnetic r-Fe2O3 or CrO2 powder. When recording, the current corresponding to the sound change is amplified and sent to the coil of the recording head, so that a concentrated magnetic field is generated in the gap of the head ferrite core. As the coil current changes, the direction and intensity of the magnetic field also change accordingly. As the tape passes through the head ferrite gap evenly, the magnetic field passes through the tape and magnetizes it. Since the left magnetic tape leaving the corresponding residual magnetism, the polarity and intensity corresponding to the original sound. The tape is constantly moving, and the sound is continually recorded on the tape.

Playback, the tape will have been recorded at the same speed recording close to the playback head gap into. Head core is made of high permeability ferrite soft magnetic material, it has little resistance to flux. Therefore, the tape recorded audio residual flux, easy to form a loop through the head iron core. Remaining magnetic flux on the magnetic tape induces a induced electromotive force with the same law of the remanent flux on the head of the reproducing head. Then amplified by the playback amplifier, sent to promote the speaker, the audio signal recorded on the tape will be restored to the original sound.