Audible Frequency Ranges of Music, Speech 

 and Noise * 



By W. B. SNOW 



This paper describes the use of an electro-acoustic system, transmitting 

 the audible frequency range almost uniformly, in determining by ear the 

 frequency ranges required for faithful reproduction of music, speech, and 

 certain noises. 



Sounds were reproduced alternately with and without filters limiting the 

 frequency range transmitted by the electrical circuit. The filter cut-offs 

 producing just noticeable changes in the reproduction were deduced from 

 judgments of listeners as to the presence or absence of filters. It was found 

 that for absolute fidelity all musical instruments except the piano require re- 

 production of the lowest fundamentals. The frequencies above 5000 cycles 

 were shown to be important, some instruments and particularly noises 

 requiring reproduction to the upper audible limit. 



Tests were made in which experienced listeners judged the degradation of 

 "quality" produced by a series of filters. The judgments showed definitely 

 that the quality continues to improve as the frequency range is extended 

 down to 80 or up to 8000 cycles. Although somewhat indefinite on cut-offs 

 outside these limits, they indicated that reproduction of the full audible 

 range was considered most nearly perfect. 



ANY sound transmission system, if it is to give faithful reproduction, 

 should transmit all the audible frequencies of a sound in their 

 proper relative intensities. To give acceptable reproduction, it should 

 transmit those frequencies considered most necessary for any particular 

 application. The audible frequency range depends upon physical 

 factors — the frequency-amplitude characteristics of a sound and the 

 hearing characteristics of the average ear — whereas the acceptable 

 frequency range must be determined by judgment when engineering 

 or economic considerations limit transmission. As engineering limita- 

 tions disappear and practical design becomes more a matter of eco- 

 nomics a knowledge of both audible and acceptable limits increases in 

 importance. 



The program of listening tests described in this paper was undertaken 

 primarily to establish the audible frequency ranges of the sounds most 

 often encountered in sound reproduction, but some tests bearing on 

 acceptable ranges were included. The sounds were transmitted 

 through an electro-acoustic system equipped with electrical filters by 

 means of which all frequencies above or below any desired cut-off could 

 be suppressed, and observers determined the high and low frequency 

 cut-offs causing just perceptible differences in the transmission. All 



* Presented at the Camden mtg. of the Acous. Soc. Amer., May 4-5, 1931. Pub- 

 lished in the Jour. Acous. Soc. Amer., July, 1931. 



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