DURATION OF STIMULUS TO PRODUCE PITCH SENSATION 299 



daily at the larger excitation intensities. In the whole audible frequency 

 range of 20 to 20,000 cycles, at the loudness level excited by 40 db above 

 threshold, 1500 different pitches are distinguishable. The maximum 

 number of changes in pitch, amounting to 1800, are experienced along 

 the 60-db loudness contour. The resolving power of the ear at a con- 

 versational loudness level of about 40 db is about three times as great as 

 at the loudness level of whispered conversation. 



Duration of Stimulus to Produce Pitch Sensation 



It has been shown experimentally that when the sounding stimulus has 

 a frequency of 1000 cycles at least 12 cycles are necessary to produce a 

 sensation of pitch and at 10,000 cycles not less than 250 cycles are 

 needed. At 1000 cycles the tone must persist for at least 0.012 second, 

 and at 10,000 cycles for 0.025 second, before the pitch sensation is 

 built up. 



TABLE VII-3 



These data show how many seconds a tone of a given frequency must last to 

 produce its pitch sensation. 



„ , „ ~ ,. . , Number of Waves Required 



Frequency of Source Duration in Seconds „. n ., , „ ?. 



H J to Give Pitch Sensation 



50 0.060 3 



200 0.022 4.4 



500 0.014 7 



1,000 0.012 12 



2,000 0.012 24 



5,000 0.015 75 



10,000 0.025 250 



Biirck, Kotowski, and Lichte [1935]. 



The experiments of Biirck, Kotowski, and Lichte [1935] show to what 

 extent a time element is involved for the identification of pitch. This 

 time element (Table VII-3) is smallest in the frequency range 1000 to 

 3000 cycles, where it is about 0.01 second. During this time a minimum 

 number of compressional disturbances must impinge on the eardrum 

 before the pitch of the incident frequency can be identified. The time 

 of adjustment of the interaural mechanism to frequency response is 

 apparently a minimum in the range of greatest aural sensitivity and 

 takes place more rapidly for high than for low frequencies. This may be 

 attributed to the variation of pitch response in time to the reflex of the 

 interaural muscles. As pointed out in a previous section, muscular 



