Magnetic Recording in Broadcasting

Abstract

IN a paper read by A. E. Barrett and J. C. F. Tweed to the Institution of Electrical Engineers on December 1, some of the methods of recording sound, especially those in connexion with their applications to Empire broadcasting, were considered. In Great Britain, very little information has been published on the subject of magnetic recording on steel tape. Dr. Stille, a German engineer, was the first to use steel tape for recording, and he made notable advances in the necessary technique. The British Broadcasting Company first tested the system in 1930 when the Empire broadcasting service was being inaugurated. Extracts from the home programmes were recorded and afterwards reproduced in the Empire transmission. The first important programme to be radiated to the Empire by this means was that on Christmas Day 1932. It included a speech by King George V. Early in 1933, Marconi's Wireless Telegraph Co., Ltd., designed a machine in which many of the mechanical difficulties experienced with earlier models were successfully overcome. It has been developed further by both the Company and the B.B.C. Magnetic recording in its simplest form can be carried out by passing a length of steel tape at constant velocity through an electromagnetic device, called a recording head, which produces variations in the magnetism of the tape. Reproduction is effected by passing the magnetized tape at the same velocity through a device called the reproducing head, which is sensitive to the changes in the magnetism in the tape. In the ideal case these correspond to the original alternations applied to the recording head. When a new record is wanted, it is necessary to remove the previous variations in the magnetism before recording. This is done by passing the tape through a 'wiping head' which strongly magnetizes the tape. The wiping, recording and reproducing heads used in the experiments described by the authors have different types of coils and pole-pieces, but are in other respects identical.