. Elements of acoustical engineering. Electro-acoustics; Sound. NONLINEARITY OF THE EAR 323 tone is shifted, due to the presence of noise, is called the masking in decibels at the frequency corresponding to that of the pure tone. The masking effect of a pure tone, a narrow band of thermal noise and a wide band of thermal noise is shown in Fig. The figures on each of the curves show the intensity level of the masking tone or noise. The ordinates, in each of the charts, show the decibels above the threshold that the various frequencies must be raised in order to be just heard in the 200 CY
. Elements of acoustical engineering. Electro-acoustics; Sound. NONLINEARITY OF THE EAR 323 tone is shifted, due to the presence of noise, is called the masking in decibels at the frequency corresponding to that of the pure tone. The masking effect of a pure tone, a narrow band of thermal noise and a wide band of thermal noise is shown in Fig. The figures on each of the curves show the intensity level of the masking tone or noise. The ordinates, in each of the charts, show the decibels above the threshold that the various frequencies must be raised in order to be just heard in the 200 CYCLE TONE i 99 / r'' .. ^ S 84 \ /^ "^ 69\ s ^ ^:; "i ^; r, ::: 54S -â ; s 1000 CYCLE TONE NOISE 140 TO 260 CYCLES 95 â 1 â - 8-; //â l-^ -- , \, 'â /'' 59 - ., V s \ ^'-â ' 44 '" :â ;â . ^â¢â¢ 'i". 7 \ /, \lo A k; v° ^. '/. k 40 ' > NOISE 1050 TOI250 CYCLES \ X 1 iV^ 33^ s /â ' '\\ ^'^ V ' ^ i ;; .'. â \^ 4^ > v ^3--'.- - r. f. 4000 CYCLE TONE IS °80 2 60 i40 â¢n 20 > y K \ \ r:5 9 â¢44 i;-* \! 100 NOISE 140 TO 1200 CYCLES ^ ^02 / <-\\ feN 40 20 / M^ â¢â ' v^^ ^ /// /⢠.'' â I^A ^â â¢^ 40-- i m 600 CYCLES. NOISE 3000 TO 3260 CYCLES NOISE 3000 TO 5500 CYCLES / > r V y ' 1 i _ \; ^' ,â ' 85^ 1 \ 1 â¢â _70. :. ', irr: fA 'â¢â :'. :â¢.: "SO V 10000 100 Fig. Masking audiograms for single frequency tones, narrow bands of thermal noise and wide bands of thermal noise. The curves are labeled in db above zero loudness. (After Fletcher and Munson.) presence of the particular masking tone or noise. For example, referring to the 4000 cycle tone having an intensity of 93 db, it is only necessary to raise a 2000 cycle tone 20 db to be heard. On the other hand, a 10,000 cycle tone must be raised 66 db to be heard. Nonlinearity of the Ear ^. â When a pure tone of a suitable in- tensity is impressed upon the ear a series of harmonics or overtones of the original frequency are heard. Furthermore, when
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