SOUND RECORDING ON MAGNETIC TAPE 



167 



Steel tape as a recording medium was suggested by V. Poulsen in 

 his U. S. patent No. 661,619-1900. Its use eliminates many of the 

 objectionable features of the wire recording system. The magnetic 

 patterns in the tape pass the pole-pieces during reproducing in the same 

 relative positions as at the time they were made. It is practical to 

 wind the tape on reels of pancake shape. Snarling difftculties en- 

 countered when using wire are thereby avoided. Thin tape permits 

 the use of smaller pulleys without exceeding the bending fatigue limit 

 of the metal. The use of tape permits the perpendicular method of 

 magnetization to be employed. High frequencies may therefore be 

 recorded and reproduced with a relatively low linear tape speed. 



Methods of Magnetization 



There are two methods of longitudinal magnetization in use, one 

 and two pole-piece recording. A detailed description of these methods 

 is given in two of the papers which have been mentioned. It will be 

 sufficient here to consider them only briefly. 



LENGTH OF TAPE 

 Fig. 1 — Longitudinal magnetization of a recording medium by a single pole piece. 

 SIG = Signal coil; DP = Depolarizing coil. 



Figure 1 shows the action taking place in recording with one pole- 

 piece. M is the recording medium and P is the recording pole-piece. 



