SOUND RECORDING ON MAGNETIC TAPE 



175 



better to favor some point slightly to the right of the crest in order to 

 avoid the danger of very strong signals operating too far down on the 

 left side of the curve. The recording current for the 1000 cycles had a 

 value 30 db below the overload so that only a small amplitude was 

 used in obtaining the data for this curve. 



If the same set of pole-pieces is used both for recording and repro- 

 ducing, there is no question of getting the reproducing pole-pieces in 

 the same alignment as the recording pole-pieces. If different sets are 

 used care must be taken to get the same alignment. 



In order to keep the signal high above the tape noise, it is desirable 

 to record so that the flux or current amplitude is independent of the 

 frequency. Since the impedance of the recording coils rises rather 

 sharply with frequency, it is necessary either to place a high resistance 

 in series with the recording coils or to connect them to a high impedance. 

 The later method is of course the more efficient. Since the energy 

 present in the higher frequencies of voice and music is usually less 

 than in the 1000-cycle region, an amplifier having a rising character- 

 istic may be used in order to record these frequencies at a higher level. 

 A corrective network may be used in reproducing to obtain the de- 

 sired frequency response. Such a procedure increases the apparent 

 ratio of signal to the tape noise. 



Reproducing 

 If the thickness of the pole-piece tips is small with respect to the 

 wave length of the signal on the tape, the voltage generated in the 

 reproducing coils is proportional to frequency, so that the coils may 

 be matched to favor the lower frequencies. If a straight line fre- 

 quency characteristic is desired, a corrective network may be used. 



20 



50 



5000 10 000 



100 500 1000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 10 — Frequency response curves obtained with the perpendicular method of 



magnetization. 



