# How does air pressure affect pitch?

• sgstudent
In summary, the length of vocal chords and atmospheric pressure both play a role in determining the pitch of a sound. In low pressures, thinner air can absorb more energy, resulting in a change in pitch. When inhaling helium, the change in gas density effectively shortens the vocal chords, altering the resonant frequencies and changing the power distribution amongst harmonics. The frequency of a sound is primarily determined by the length of the vocal chords, and the energy of a particular harmonic is related to the frequency. Attenuation of sound in air is mainly affected by humidity, and changes in density can also affect pitch.
sgstudent

## Homework Statement

I thought that only the length that the sound travels affects the pitch. However, in low pressures/breathing helium the distance traveled by the gas is the same so how is pitch affected?

none

## The Attempt at a Solution

this is what i found from another post "That's true, but the atmospheric pressure has as much to do with propagation of the sound as the pitch. The frequency is primarily determined by the length of the vocal chords; the longer they are, the lower the frequency. Thinner air, though, absorbs the energy of the sound before it can go very far.
That's the reason that people sound so 'duckish' after inhaling helium. The change of ambient gas density effectively (but not physically) shortens the chords. That is because the initial vibrations are attenuated according to the density of the medium that they are propogating through."

I don't understand how thin air can absorb more energy than normal air and how does decreasing the energy decreases the pitch shouldn't it only decrease the loudness since there is less energy?

Thanks for the help!

sgstudent said:
I don't understand how thin air can absorb more energy than normal air
Well, in thin air, the sound will travel less far. And the energy must go somewhere, so what must we conclude?

sgstudent said:
and how does decreasing the energy decreases the pitch shouldn't it only decrease the loudness since there is less energy?

Thanks for the help!
I'm not sure what you mean here. Do you mean decreasing the energy of vibrations which caused the sound? Think about the simple case of an oscillating string. How is the energy of a particular harmonic related to the frequency?

BruceW said:
Well, in thin air, the sound will travel less far. And the energy must go somewhere, so what must we conclude?

I'm not sure what you mean here. Do you mean decreasing the energy of vibrations which caused the sound? Think about the simple case of an oscillating string. How is the energy of a particular harmonic related to the frequency?

Hi why would sound travel less far in thin air? Since when we take a breathe and speak, the air that vibrates starts from the lungs to mouth has traveled the same distance. So how should the pitch change?

BruceW said:
Well, in thin air, the sound will travel less far. And the energy must go somewhere, so what must we conclude?
As I understand it, attenuation of sound in air is chiefly a function of humidity. For a given humidity, density has not much to do with it. The attenuation that results varies according to frequency, so it will change the pitch. See e.g. http://www.kayelaby.npl.co.uk/general_physics/2_4/2_4_1.html
Helium does not, strictly speaking, change the pitch of the voice. It alters the resonant frequencies within the mouth and throat, so changes the power distribution amongst the harmonics. Google "helium pitch".

What haruspex said.

If your vocal chords vibrate at 500Hz then 500Hz is what reaches your ears regardless of the density or speed of sound of the air/helium.

## 1. How does air pressure affect pitch?

Air pressure affects pitch by changing the speed of sound waves. When the air pressure is higher, the molecules are closer together, making it easier for sound waves to travel. This results in a higher pitch. Conversely, when the air pressure is lower, the molecules are more spread out, making it harder for sound waves to travel and resulting in a lower pitch.

## 2. Does air pressure affect pitch differently in different environments?

Yes, air pressure can affect pitch differently in different environments. For example, at higher altitudes where the air pressure is lower, the pitch of sound will be lower compared to at sea level. This is because the air molecules are more spread out at higher altitudes, making it harder for sound waves to travel.

## 3. How does temperature affect the relationship between air pressure and pitch?

Temperature can have an impact on the relationship between air pressure and pitch. As temperature increases, air molecules move faster and are more spread out, resulting in a lower air pressure. This can cause a decrease in pitch. However, the effect of temperature on pitch is much smaller compared to the effect of air pressure.

## 4. Can air pressure affect the pitch of all sounds?

Yes, air pressure can affect the pitch of all sounds. This is because all sounds are created by vibrations in the air, and air pressure has a direct impact on how fast these vibrations can travel. Therefore, changes in air pressure will result in changes in pitch for all sounds.

## 5. Is there a specific measurement for how air pressure affects pitch?

Yes, there is a specific measurement for how air pressure affects pitch. It is called the speed of sound, and it is typically measured in meters per second. The speed of sound varies depending on air pressure, temperature, and other factors, but it is generally around 343 meters per second at sea level.

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