326 



SPEECH, MUSIC AND HEARING 



either very small pickup distances or directional collecting systems in the 

 monaural collection of sound. 



13.12. The Frequency and Volume Ranges of Speech and Music and 

 the Effects of Frequency Distortion upon Reproduced Sound. — The fre- 

 quency range of the average normal ear is from 20 to 20,000 cycles. The 

 frequency range of most reproducing channels such as the radio, the tele- 

 phone, the phonograph and the sound motion picture is considerably less 

 than that of the hearing range of the ear. It is interesting to note the 

 effect of the frequency range upon the intelligibility of speech and the 

 quality of music. 



The frequency " and volume ranges of speech and orchestral music 

 are shown in Fig. 13.7. The reproduction of speech with perfect fidelity 



2000 



100 

 TREIQUENCY 



1000 

 IN CYCLES PER 



.002 



.0002 ^ 



00002 



Fig. 13.7. 



Frequency and volume ranges of speech and music. (From Bell Laboratories 

 Record, June, 1934.) 



requires a frequency range of from 100 to 8000 cycles and a volume range 

 of 40 db. The reproduction of orchestral music with perfect fidelity 

 requires a frequency range of from 40 to 14,000 cycles and a volume range 

 of 70 db. 



The effect ^^ of reducing the high and low frequency range upon speech 

 articulation is shown in Fig. 13.8. It will be seen that a relatively high 

 articulation can be obtained with a very narrow transmission band. How- 

 ever, the quality of the reproduced speech is very much impaired by 

 transmission over a narrow frequency band. A limited range may be 



" Bell Laboratories Record, Vol. 12, No. 6, p. 314, 1934. 



^^ Fletcher, " Speech and Hearing," p. 280, D. Van Nostrand Co., New York. 



