1. When recording, the sound is converted into an audio signal through the microphone. After passing through the recording amplifier, the amplified audio current and the bias current pass through the coil of the recording head, and a magnetic field varying with the audio current will be generated at the gap of the magnetic head.

2. The gap between the magnetic tape and the recording head is close to each other and keeps moving at the same time, so that the changing magnetic field lines pass through the magnetic tape in front of the head gap to form a closed magnetic circuit and magnetize the magnetic tape. Complete the recording.