Sound Recording on Magnetic Tape

A SYSTEM of recording speech magnetically on a steel wire was invented by Poulsen almost forty years ago. The wire was drawn past a pair of pole-pieces surrounded by coils carrying a speech current. A magnetic pattern corresponding to the current was thus impressed on the wire. When the wire thus magnetically treated was again drawn past the pole-pieces a current corresponding to the recording current was induced in the surrounding coils. It was common practice to place the pole-pieces on opposite sides of the wire and offset with respect to each other. The magnetic pattern in the wire thus consisted mainly of a variation in the intensity of magnetization, the direction of the magnetization being substantially parallel to the axis of the wire. This method of putting the record on the wire is known as longitudinal magnetization. With such a system the wire must travel at a very high speed if high frequencies are to be recorded and reproduced. It was customary to use speeds of from six to ten feet per second. By using tape instead of wire, the recording and re165