Sunday 2 November 2014

waves - Sound pitch: why the louder the higher?


I have been wondering for years why, listening to any music (or simply to a single tone), better with headphones/earphones, if the volume is very low (almost inaudible: 20-30 dB SPL), each audible note of the same music sounds flatter than when played at a far higher volume (70-80 dB SPL), using the same equipment: I guess about 20 cents sharper, when far louder. It is like a "static" Doppler effect depending on loudness and not motion, but I am surely talking nonsense. Please, consider that I am absolutely ignorant of Physics, although I am a musician! Thanks for your help.



Answer



The perceived pitch of tones with a high frequency (above about 2 kHz) tends to increase when their sound pressure level is increased. This is a known psychoacoustic effect that agrees with your description. However, the perceived pitch of tones with a low frequency (e.g., 200 Hz) tends rather to decrease when their sound pressure level is increased. This appears to be due to an imperfect compensation for the more substantial effect an increased sound level has on the neural excitation pattern along the basilar membrane of the ear. The effect varies to some extent between listeners.


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