SOUND RECORDING ON MAGNETIC TAPE 



169 



these changes in the direction of the flux while passing from 1 to 3, 

 a modulation of the flux 3 might be expected to leave an undistorted 

 record on the medium as was the case with one pole piece recording. 

 However, in the case of two pole-pieces, the elements still must pass 

 the pole-piece P2 where the flux 4 is approximately perpendicular to 

 the medium. After passing the pole-piece Pi the record is subjected 

 to the flux 5 which is in the opposite direction to the recorded flux. 

 The record which was made by the flux 3 is therefore distorted by 

 fluxes 4 and 5. This distortion is greater than it is for one pole-piece 



LENGTH OF TAPE 

 Fig. 2 — Longitudinal magnetization of a recording medium by two pole pieces. 



recording. In practice the stray fluxes 4 and 5 are sufficiently small 

 so that the distortion introduced may be tolerated in exchange for the 

 improved frequency response which is obtained with two pole-piece 

 recording. 



Figure 3 shows the action taking place where cross-magnetization is 

 used. It is here assumed that the recording medium has been pre- 

 viously magnetized so that the residual magnetization is in the di- 

 rection indicated by the upper arrows at the left. W represents the 

 width of the recording medium which in this case is a steel tape. It will 

 readily be seen that if Wi's, very large there will be considerable spread- 



