Chapter 7 - Disc and Tape Recording

Abstract

The system of disc recording used a groove cut in shellac (or later, vinyl) disc and modulated by the sound waves. For good-quality recording, the bass amplitude must be reduced and the treble frequencies boosted on recording and the opposite actions carried out on replay. Electrical recording and reproduction offer much more control over the process. Disc stereo recording uses a cutting head whose stylus can be vibrated in two directions that are at right angles to each other, cutting tracks in the walls of the groove. Tape and cassette recording of sound is not new, but the methods that are used to make the sound of acceptable quality are of recent origin. All magnetic recording makes use of a magnetic material being moved past a recording/replay head which consists of a metal core with a narrow gap and a coil of wire, and the construction of this head is very exacting if good-quality recording is required. Noise is the enemy of all recording and broadcasting systems. For professional recording, the use of wide tape overcomes the problem to a considerable extent because a wider tape has a larger magnetized area and so produces a larger signal that “swamps” the noise. Noise-reduction systems operate on the principle of selectively boosting the amplitude of the recorded sound when it is recorded and decreasing it on replay, and a particularly effective method of doing this concentrates the boosting and reducing actions on the frequency range that is the most affected.