REPRODUCTION OF MAGNETICALLY RECORDED SIGNALS 



1155 



Thickness Loss = 20 logio 



27r5/X 



,-2rhl\ 



db 



(5) 



where X is the recorded wavelength and 5 is the thickness of the recording 

 medium. This function is plotted in Fig. 7. 



Comparison with Experiment 



The most elementary consideration of the magnetic recording process 

 indicates that when the recording signal current is held constant the open 

 circuit reproduced voltage should be a function of frequency, increasing 

 by 6 db for each octave increase in frequency. Experimental response curves 

 tend to show this 6 db per octave characteristic when the recorded wave- 



10 



15 



20 



25 



30 



35 



40 



45 



0.02 0.04 0.06 0.10 0.2 0.4 0.6 0.8 1.0 2 4 6 8 10 



6/\ 



Fig. 7 — Computed thickness loss as a function of 5/X. 



20 



length is moderately long and the frequency moderately low. This makes 

 it possible to draw a 6 db per octave line on the measured response char- 

 acteristic in such a way as to coincide with the low-frequency part of the 

 measured response characteristic. As the frequency is increased the meas- 

 ured curve tends to fall more and more below the 6 db per octave line. This 

 is because several kinds of loss come into play as the wavelength decreases 

 or as the frequency increases. Among these losses are: 



1. Self demagnetization, 



2. Eddy current and other losses in the recording and reproducing heads, 

 and 



3. Gap loss due to the finite scanning slit in the reproducing head. 



The work presented in the first sections of this paper indicates that the 



