How was magnetic sound recording carried out?

Magnetic recording and reproduction of sound information includes the following physical processes:
♦ conversion of sound mechanical vibrations into electrical vibrations of sound frequency;
♦ transformation of electrical oscillations into an alternating magnetic field, the shape and intensity of which corresponds to changes in electrical oscillations;
♦ fixation of the magnetic field on the sound carrier, i.e. its magnetization;
♦ reproduction of the recording by inverse transformations of the magnetic field of the sound carrier into electrical and then sound vibrations.
The phenomenon of magnetization and is used in tape recorders. The microphone converts the audio signal into an electrical signal. This signal is recorded with the help of a magnetic head on a moving pickup (magnetic tape), the working layer of which consists of particles of a magnetically hard ferromagnet, as a result of which a magnetic trace (residual magnetization) remains on the tape. The recording obtained on a sound carrier is called a phonogram.