10 minutes ago, studiot said:

A good example of the variable speed is the so called helium speech experienced by divers breathing specialist atmospheres, due to the change of density and therefore speed in the medium.

I'm not sure that is a good example because it doesn't change the fundamental frequency - the vocal cords still resonant at (approximately) the same frequency. It just changes the resonant effects of the vocal cavities, so we hear different harmonics.

21 minutes ago, Strange said:

I'm not sure that is a good example because it doesn't change the fundamental frequency - the vocal cords still resonant at (approximately) the same frequency. It just changes the resonant effects of the vocal cavities, so we hear different harmonics.

Actually, helium doesn't change the resonant wavelength of the vocal cavities, but since sound travels faster in helium, the frequency has to be higher to maintain the same wavelength. Similarly, harmonics are also shifted higher in frequency.

The frequency remains higher if the sound is conducted to normal air.

13 minutes ago, Carrock said:

Actually, helium doesn't change the resonant wavelength of the vocal cavities, but since sound travels faster in helium, the frequency has to be higher to maintain the same wavelength. Similarly, harmonics are also shifted higher in frequency.

The frequency remains higher if the sound is conducted to normal air.

And the reason it isn't a good example, is that it is more complex than it seems!

9 minutes ago, Strange said:

And the reason it isn't a good example, is that it is more complex than it seems!

Yes wave transmission is more complicated (I try to use the word complicated in preference to complex for mathematical association reasons).
Particularly as and when you introduce Relativity into the equations of motion (as Dirac's equation is more complicated than Schrodinger's).

 

However there is no medium induced Doppler effect, the effect of the medium was an off topic aside.
Nonlinearity of the medium is another complication, as is the nature and characteristic of the signal itself.

Edited November 30, 20187 yr by studiot

20 minutes ago, studiot said:

However there is no medium induced Doppler effect, the effect of the medium was an off topic aside.

This is a key point that Itoero needs to understand. 

21 minutes ago, studiot said:

I try to use the word complicated in preference to complex for mathematical association reasons).

Good point!

On 11/30/2018 at 2:38 PM, Strange said:

This is a key point that Itoero needs to understand. 

What is Itoero doing at the moment? Still trying to understand? I wonder why he seems to have left the thread.