2.2.1 Recording principle

A magnetic carrier is moved across an electro-magnetic recording head. The head produces a magnetic field that varies according to the signal it receives from the recording device. This magnetic information is “frozen” within the magnetic carrier as it passes the recording head. The recorded signals can be retrieved by running the carrier across a replay head (sometimes identical with the recording head) that picks up the magnetic field and converts it back into an electric signal. With analogue audio tape recorders the head is stationary. Analogue video signals, as well as digital audio and video signals, require a considerably higher bandwidth than the analogue audio signal. This is achieved by greatly increasing the recording speed. This increase in speed cannot be done by simply moving the tape faster as the amount of tape required is excessive. The problem is generally solved by a rotating head which writes across the width of the tape with high speed, while the linear speed of the tape is much slower.

It is important to understand that, in order to optimally retrieve the signal from a tape, an intimate tape-to-head contact is essential, which is one of the reasons for keeping tapes, machines, as well as storage and handling areas, clean (see 3.5.1 and fig. 25).

For the specifics of hard disk recording, see 2.2.2.

By using the Kerr effect, magnetic information can also be read optically. This principle is used with magneto-optical carriers ( It is also employed in the retrieval process of high-density computer back-up tapes. Reading conventionally recorded audio tapes by using this principle has not developed beyond an experimental state.