To record a tape, the first step is erasure of the preexisting recording. To accomplish this, a bias oscillator generates a current which is used to feed the erase head. This removes any magnetism that might already be present on the tape.
The next step depends on whether the machine is a stereo or mono recorder. A mono recorder will record with two tracks, one for each side of the tape. A stereo recorder uses four tracks, one for each channel on each side. The recording and playback heads are placed in such a way that side one uses the first and third tracks, while side two uses the second and fourth tracks (see illustration below). This way, when the tape is turned over to the other side, the opposite two tracks are used for recording and playback.
The recording process is relatively simple. The voice or music is fed into microphones, which is then converted to electrical current and amplified as with disc recording. The signal is then fed into an electromagnet called the recording head. Varying electrical currents produce varying degrees and patterns of magnetism in the tape. Playback is exactly the reverse. The tape's magnetism, as it passes over the playback head, induces electrical current in the electromagnet. This signal is then amplified and reproduced via speakers. See illustration below for an explanation of the process.
It is important to realize that placing a magnet close
to a tape will cause erasure.