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BELL SYSTEM TECHNICAL JOURNAL 



from groove to groove. In order that a lateral oscillation in a groove 

 may represent constant intensity of sound or a constant energy over 

 a range of frequencies, not the amplitude of the oscillation but the 

 velocity, which is proportional to the product of the amplitude and 

 the frequency, must be maintained constant. With the characteristic 

 shown with these recorders, constant velocity is obtained from about 







100 500 1000 



FREQUENCY 



Fig. 2 — Typical frequency characteristic of a commercial recorder. 



250 cycles to 5,500 cycles. Below 250 cycles an approximately 

 constant amplitude is obtained. If, therefore, sounds of constant 

 absolute intensity are to be recorded over this range of 30 to 250 

 cycles, there is equal tendency for sounds of the different frequencies 

 in this range to over-cut the record groove. It may be corrected in 

 reproduction by a suitable electric network. Such a network will 

 increase the subsequent amplification required but, as this additional 



Fig. 3 — Frequency characteristic of a laboratory model recorder. 



amplification occurs in the first stages, it is not expensive. Practically 

 it has not been found necessary or desirable to introduce such a 

 corrective network since the correction has been largely cared for by 

 the characteristics of the pickups used. 



Recent development studies have established the possibility of 

 flattening the response at the low frequency end and of raising the 



