160 BELL SYSTEM TECHNICAL JOURNAL 



the low frequency range be lowered to 25 or 30 cycles, a noticeable 

 improvement will be obtained with some classes of music, whereas 

 if the upper limit be increased to 8,000 or even 10,000 cycles, the 

 naturalness and smoothness of practically all classes of reproduction 

 will be noticeably improved. 



A second important requirement in the judgment or analysis of 

 any such system is that the ratio of output to input shall not vary 

 over the range of currents or loudnesses (as well as frequencies) from 

 the minimum up to the maximum used. If this requirement is not 

 met, sounds or frequencies not present in the original reproduction 

 will be introduced. This type of distortion has probably been heard 

 by all of us in listening to an overloaded vacuum tube amplifier and 

 is often referred to as "non-linear" distortion. 



A third requirement not entirely disassociated from the first two 

 is that any shifts in the phase relations shall be proportional to 

 frequency. 



Our judgment of the degree of perfection needed in sound repro- 

 duction systems is changing and growing more critical, so that what 

 seemed excellent yesterday may be only fair today and tomorrow 

 may seem intolerable. It is therefore necessary that our consideration 

 and analysis be continually more searching and fundamental. 



Of the eleven links in the chain of apparatus required for electric 

 "wax" recording and reproduction, only five are peculiar to the 

 "wax" method. These are the electromechanical recorder, "wax" 

 record, the copying apparatus, the "pressing" and the pickup or 

 reproducer. The extent to which the "wax" method is capable of 

 the highest quality of reproduction will be disclosed by an examination 

 of these five links. Any consideration of the practical advantages or 

 disadvantages of the method can logically follow this examination 

 into the quality possibilities. 



The consideration which follows refers to the so-called "lateral" 

 cut record; that is, a record in which the groove is of constant depth 

 and oscillates or undulates laterally about a smooth spiral. This is 

 the type used in the Western Electric Company disc record type of 

 synchronized motion picture system. Some, but not all of the con- 

 siderations and conclusions might apply to the "hill and dale" type 

 record. It is not the purpose of this paper to consider the relative 

 characteristics of "hill and dale" and "lateral" "wax" records. 



Electromechanical Recorder 



It is the task of the electromechanical recorder to take power from 

 the amplifier and drive a mechanical recording stylus. The present- 



