11

When I produce a 440hz signal is it in all conditions (air-pressure, medium or compositon of the athmosphere, on a mountain, on alien planets etc.) perceived as the same note? Assuming a human can survive in all those mentioned conditions of course.

I only ask about the frequency, which is the pitch. Not about other parameters of the tone.

  • You might find some detailed answers on Physics.SE; tho' possibly with more math than you want :-) – Carl Witthoft Nov 29 '15 at 13:51
  • 2
    Not related to the acoustics of the situation, but the perception of pitch can vary from person to person or for one person in their lifetime. Those who grow up with perfect pitch sometimes find their perceptions change as their basilar membrane stiffens with age. 440 may sound like A in one's youth and then A# with age. – Todd Wilcox Nov 29 '15 at 20:27
  • 1
    @CarlWitthoft : Math is good. Always. – nilshi Nov 30 '15 at 9:01
  • @ToddWilcox One of my friends reports that and it spoils his enjoyment of playing the piano as he does not hear the note that he expects to hear. Conversely, I have never had perfect pitch and my piano which is tuned a little flat is not an issue until another instrument is involved. – badjohn Apr 20 '17 at 14:23
17

The perception of a pitch is due to the frequency of vibration of the hairs in the cochlea (the spiral-shaped organ in the inner ear), which is, in turn, driven by the vibration of the eardrum. Anything that drives the eardrum at a given frequency, say 440 Hz, will be perceived as the same pitch, regardless of medium.

What the medium does affect, however, is the speed of sound (v), which determines the relationship between frequency (f) and wavelength (L) according to the equation v = f * L. The physical mechanisms of many instruments are such that they create a tone of a fixed wavelength rather than a fixed frequency. For example, an organ pipe will create a standing wave with a wavelength determined by the length of the pipe. If the pipe is tuned to produce 440 Hz at room temperature, than changing the temperature of the air -- or its humidity, density, or even completely changing the medium -- will cause the speed of sound to change. As a result, the frequency it produces will be different, and it will be perceived as a different pitch. Organ tuners are always careful to tune organs at room temperature, and if the organ is played at a different temperature, it may sound out of tune.

Incidentally, this is also why breathing helium creates such a funny sounding voice. The shape of the mouth and the tension of the vocal cords fix the wavelengths that are produced, but the lighter medium allows the sound waves to travel faster, so they have a higher frequency. When the waves exit your mouth into the "regular" atmosphere, they retain their frequency, and it is the wavelength that changes to accommodate the slower speed of sound.

  • This confirms my own hypothesis (what matters is the frequency that drives the ear drum). I marked the question as answered and gave it an upvote. Adding some source and quotes would be nice to have though. – nilshi Nov 30 '15 at 8:58
  • For the opposite effect to helium, you can use sulfur hexafluoride in place of helium. You might like to take independent medical advice first. – badjohn Apr 20 '17 at 14:29
7

If you can cause the tympanic membrane of a normal-hearing human to vibrate 440 times per second, they will "hear" the pitch we call A4. So, there are two ways to go with your question. A device that is designed to produce 440 Hz here on Earth is designed to cause normal earth air at normal air pressure to vibrate 440 times per second. In significantly denser air, that device will not be able to vibrate the medium as quickly as it's designed to do, and thus the pitch perceived will be lower. The opposite is true for lighter air. If there's no medium at all, such as empty space or a planet with no atmosphere or liquid, then there can be no sound.

However, another approach to the question is to assume the device is capable of vibrating any medium 440 times per second. If the device produces 440 Hz with respect to the medium, then the perceiver will hear an A4.

The difference in air pressure on various parts of the earth isn't large enough for major discrepancies, but you can hear how much lower pitch sounds when the medium is water.

It's worth noting that most pitched sound contains way more than a single frequency, so the more noticeable effect would probably be timbral, as higher overtones will be more able to excite a thicker medium.

2

For the sake on completeness, I will add that the relative speed between the generator of the sound and the observer will change the pitch, due to the Doppler effect.

  • Does it change anything for your ears reference frame if there is a Doppler effect or not? – nilshi Nov 30 '15 at 14:46
  • Yes, it does. Remember the police car moving : high pitch when coming toward use, lower pitch when moving away. – leo Nov 30 '15 at 15:55
0

In short: no. "The same note" is a musical concept, and playing 440Hz in a baroque concert with A=415Hz tuning will not be perceived as an A. As long as your question is about a "note", a musical concept, rather than an acoustical phenomenon, the answer is clearly "no". Even with an A=440Hz tuning, 440Hz might indicate a double-flatted B instead of A, again a different note (as notes have a role in scales).

Now if you are not talking about note but only perceived pitch as an acoustical rather than musical phenomenon, perceived pitch, like perceived color, depends on the backdrop. If you are talking in a helium atmosphere with others, your pitch perception and evaluation will adapt to their speaking voices.

  • There's some cool research that illustrates the point — see the video to the right. – LiberalArtist Nov 29 '15 at 19:05
  • 440Hz = A was implicit in my question – nilshi Nov 30 '15 at 8:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.