How Are Music and Video Recorded With the Help of Magnetic Tape?

When it comes to the recording of music, magnetic tape recording proved to be the foundation for everything we know about the industry today. It was the first mode of recording music with the ability to store a certain amount of bulk data. There are two primary realms that depend on magnetic tapes, one being music and the other being video recording. Before the advent of the CD, the Internet and online music and video, the most popular form of purchasing these art forms was music cassettes and VHS tapes.

Before we take a look at how this technology is employed, let’s first take a look at the properties of a magnetic tape itself.

casette

(Photo Credits: Pixabay)

The Tape

A magnetic tape is pretty simple. The tape usually has a plastic material used as a base, and on top of this base, a coating of ferric oxide powder is applied. The oxide is usually mixed with a binder, which helps the ferric oxide stick properly to the plastic film. A dry lubricant is also used to prevent the film from tearing over time due to friction. The ferric oxide must not be confused with iron oxide. Iron oxide, also known as rust (FeO), is not Ferric Oxide (Fe2O3), which is another oxide of iron. Other common names for ferric oxide are Maghemite and gamma ferric oxide.

Audio Magnetic Tape Magnetic Foil Music Cassette

The oxide used has a unique property in that it is a ferromagnetic material. A ferromagnetic material can be defined as an object that can be permanently magnetized unless and until the magnetization is removed. This gives the magnetic tape two fundamental properties. The first one is that anything can be recorded onto the tape and the tape will be able to play it back anytime we want to hear a particular song. The second important property is that the data can be erased by passing a magnet through the tape, which would remove the magnetization that is present. This would make the magnetic tape highly reusable.

Working off a Tape Recorder

The simplest things in life are truly simple, a fact that does extend to the tape recorder. Everything from the early and most popular portable music device—the Walkman—to the high-end audiophile decks of the present generation, designers have tried to keep it simple. To encapsulate the whole tape recorder mechanism, it involves the use of an electromagnet to magnetize the oxide on the film. The electromagnet is usually a tiny pin-shaped head. The electromagnet consists of an iron core wrapped in wire. During recording, the audio signal is sent through the coil of the wire to create a magnetic field in the core. At the gap between the electromagnet and the magnetic tape, a magnetic flux is formed. At the gap, the magnetic flux forms a fringe-like pattern that helps magnetize the magnetic tape. This magnetization helps imprint the data onto the tape.

megnetic tape diagram

(Photo Credit : Asenine/Wikimedia Commons)

Now that we have some idea as to how the data is stored on the magnetic tape, how is it possible to read this data and play back the music? This is where the tape head action comes into play. The tape head consists of circular rings with wires around them, similar to that of the electromagnet used for recording. The only difference is that the reverse applies when playback of the song occurs. Since the magnetic tape already consists of a certain level of magnetization as it passes through the tape head, it creates a change in the magnetic field around the tape head. According to the laws of electromagnetism, when there is a change in magnetism around a conductor, it induces a certain electric current in the conductor. This is what happens to the tape head as each part of the magnetic tape is magnetized differently; it continually produces an electric current of varying intensity. Now, the electric current that is picked up is processed by the music player, and we get to hear the song!

Now that we have a fair idea of how music is recorded and read from a magnetic tape, let’s now take a more detailed look at how the data can be erased from the magnetic tape. There is a specific part known as the eraser head that is responsible for this. The eraser head produces a high-frequency AC magnetic field on to the tape. This AC magnetic field is many times stronger than the magnetized tape, which scrambles the previously oriented magnetic lines in the tape. It must be noted that the magnetic field does not demagnetize the tape, but merely scrambles the tape’s magnetism so that new data can be magnetized onto it again. In conclusion, the next time you come across a mixtape cassette, you will know that it took a lot more than just a musician to get those tunes on the tape!

References:

  1. Hyper Physics
  2. Hyper Physics
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About the Author:

Venkatesh is an Electrical and Electronics Engineer from SRM Institute of Science and Technology, India. He is deeply fascinated by Robotics and Artificial Intelligence. He is also a chess aficionado, He likes studying chess classics from the 1800 and 1900’s. He enjoys writing about science and technology as he finds the intricacies which come with each topic fascinating.

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