The unique feature of a video-tape recorder (VTR) is that it plays back both sound and picture. It is mainly used to record television programmes as magnetic patterns and play video cassettes. But how does the video-tape recorder work?
A video-tape is a band of plastic tape. On one side, it is coated with a film of magnetic iron oxide whose thickness is about one-five thousandth of a centimetre. The width of the tape is about 1.25 to 2.5 cm. For recording a programme, the tape is run by a magnetic video tape recorder.
A television camera changes an image into electrical signals. At the same time, a microphone changes sound into electrical signals. These signals are then fed into the recorder. The VTR contains recording heads that convert the signals into varying magnetic fields. As the magnetic tape passes these heads, they produce magnetic patterns on the tape. This tape can then be used to reproduce the original sound and picture. When the tape is played back, the changing magnetic fields of the pattern of iron oxide particles create weak currents which exactly correspond to the recorded sound and picture.
The sound and picture signals are kept separated in the recorder, and are recorded on to different parts of the tape. Usually, the sound signal is recorded on to a narrow track at the top of the tape. The image signal is recorded on to a wider track in the middle of the tape. A control signal is recorded along the bottom of the tape. Television studios generally use 5 cm-wide tape. The tape moves at a speed of 37.5 cm a second.
The head that records the image signal rotates, as the tape passes by it. As a result, the recording is made in diagonal bands across the tape. This allows more information to be stored on a given length of tape.
Video tapes are used to record and reproduce various television programmes. They are also used for the reproduction of sport events during a live broadcast. Video tapes are also used in slow motion and stop-action techniques. Nowadays video discs having pictures as well as sound recordings are also available to see a film on the disc, by playing it on a video disc player connected to a television set.