Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 322 SPEECH, MUSIC AND HEARING it will be seen that for a 50 cycle tone the intensity required to reach the threshold of hearing is 250,000 times that required for a reference 1000 cycle tone. Change of Pitch with Loudness. — Frequency of a sound wave is the number of cycles per second executed by the particles of the medium in which a sound is being propagated. Pitch is that subjective quality of a sound which determines its position in a musical scale. Pitch may be measured as
Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 322 SPEECH, MUSIC AND HEARING it will be seen that for a 50 cycle tone the intensity required to reach the threshold of hearing is 250,000 times that required for a reference 1000 cycle tone. Change of Pitch with Loudness. — Frequency of a sound wave is the number of cycles per second executed by the particles of the medium in which a sound is being propagated. Pitch is that subjective quality of a sound which determines its position in a musical scale. Pitch may be measured as the frequency of a pure tone having a specified sound pressure which seems to the average ear to occupy the same position in a musical 100 200 FREQUENCY 500 1000 CYCLES PER SECOND 2000 Fig. Contours of constant loudness level. Curves show the amount by which the pitch of a pure tone of any frequency is shifted as the tone is raised in loudness level from 40 to the level of the contour. For example, a 100-cycle tone will be changed ten per cent downward in pitch if raised from a loudness level 40 to a loudness level 100, but a SOO-cycIe tone will be changed only two per cent for the same loudness level increase. (After Snow.) scale. Thus it will be seen that there is definite distinction between fre- quency and pitch. For example, a tone of a fixed frequency of a few hun- dred cycles decreases in pitch as the intensity is increased. The change ^ in pitch with loudness is shown in Fig. Masking ^'^ — The reduction of the ability of a listener to hear one sound in the presence of other sounds is known as masking. In testing the masking properties of a sound, pure tones are generally used as the masked sound. The number of decibels that the threshold level of a pure 3 Snow, W. B., Jour. Acous. Soc. Amer., Vol. 8, No. 1, p. 14, 1936. ' Wegel and Lane, Phys. Rev., Vol. 23, No. 2, p. 266, 1924. ^ Fletcher and Munson, Jour. Acous. Soc. Amer., Vol. 9, No. 1, p.
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