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BELL SYSTEM TECHNICAL JOURNAL 



which the transmission system needs to accommodate is considerably nar- 

 rower than the intensity range to which the ear can respond. 



In the first place, the range of program volum.es to which the ear can 

 respond is much less than the range of single-frequency intensities shown by 

 the curve. Program waves are in general very irregular in shape, and even 

 at constant volum.e contain large and small peaks differing in amplitude by 

 many decibels. The range between the volum.e at which the highst peaks 

 reach the maximum instantaneous intensity which the ear can tolerate and 



TYMPAtJI 



BASS DRUM — 

 SNARE DRUM- 

 14" CYMBALS- 



BASS VIOL- 

 CELLO 



PIANO 



VIOLIN 



BASS TUBA-- 



TROMBONE 



FRENCH HORN- 

 TRUMPET 



BASS SAXOPHONE 



BASSOON 



BASS CLARINET 



CLARINET 



SOPRANO SAXOPHONE- 

 OBOE 



FLUTE 



PICCOLO- 



MALE SPEECH- 

 FEMALE SPEECH- 



FOOT STEPS 



HAND CLAPPING- 

 KEY JINGLING 



500 1,000 



FREQUENCY IN CYCLES PER SECOND 



5,000 10,000 20,000 



Fig. 7 — Audible frequency ranges of music, speech, and noise 

 Observers voted for entire band by ratio of 60 to 40 over band shown by extremities 

 of lines, and by ratio of 80 to 20 over band indicated by circles. Broken lines show range 

 of noise accompanying music. 



the volume at which the smallest peaks are just above the threshold of audi- 

 bility is therefore less by a number of decibels than the intensity range of 

 the ear as measured by single frequencies. 



In the second place, the volume range of the usual program material 

 has definite limits. Measurements have shown that a large symphony 

 orchestra produces a maximum volume range of about 70 decibels.'* The 

 volume range of most other types of program is considerably less than this, 

 for example, being only about 25 to 30 decibles for dance music and as little 

 as about 15 decibels for much of the dialogue of actors in radio drama. 



