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I am a Physics student who also love music and learned a little bit about Medical Physics. I know that the basilar membrane in the cochlear duct enables us to distinguish different frequencies. The different parts of the basilar membrane have different resonance frequencies and this leads to frequency dispersion.

I've also learned that the pitch of a tone is determined by the fundamental frequency, and the overtones just add timbre to the sound, and are difficult for common people to hear separately.

I think the above implies our ears are more sensitive to lower frequencies. However, this is obviously not true when we listen to a symphony, in which I think most people are more "sensitive" to the higher parts. And I think this is the reason while the melody is usually in the highest part in a song.

So I am confused. Are our ears more sensitive to high frequencies or lower frequencies? Is there a biological explanation of why we usually tend to hear the highest-pitch part of a piece of music?

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Short answer
Our ears are most sensitive to the mid-frequencies.

Background
There are different ways of assessing sound level. The physical one simply determines the physical sound pressure level (SPL) in which all the frequencies weigh equally. This is referred to as C-weighting and is expressed in dB SPL.

Our ears, however, are most sensitive to intermediate frequencies, peaking at around 4 kHz (Fig. 1). The frequency weighting that takes this into account is dBA weighting.

The reason why we are most sensitive to mid-frequencies can be sought in the fact that sounds with frequencies around 4 kHz are amplified in the middle ear canal through the process of resonance. In effect, they are perceived 10 to 20 dB louder than other audible frequencies. The pinna also affect resonance and hence the outer and middle ear together join forces to create humps and bumps in the equal-loudness curves.


dBA
Normal equal–loudness-level contours for pure tones. source: Duncan (1996)

Reference
- Duncan, High Performance Audio Power Amplifiers For Music Performance and Reproduction (1996): 1-18

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  • $\begingroup$ Maybe "high middle" frequency , as I remember middle "C" is 512 Hz. $\endgroup$ – blacksmith37 Sep 25 at 22:03

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