I've come across a couple of videos where some interesting sounds are produced using ice. (Click on the images to see the video.)

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Here, they drop a block of ice into a deep crevice and as the block falls, you can hear some strange sounds. These sounds remind me of some sound effects in old cartoons and sci-fi movies. The pitch of the sounds start high and end up low. Is this some kind of doppler effect?

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Here, there's a man performing 'nordic skating', making the same sounds as he skates on top of a thin ice sheet. Maybe they are caused by the cracking ice. But why does that sound like this?

There are some other videos too, where they skip stones on frozen lakes.

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Here the ice makes some high-frequency sounds which correspond to the chirping of birds.

What are these sounds and why do they sound the way they sound?

  • $\begingroup$ If air is pushed through a thin slit or many small holes with varying pressure, it makes a similar sound. I remember hearing sounds like these while quickly squeezing an empty talcum powder container. $\endgroup$ – Superfast Jellyfish Mar 6 '20 at 7:22
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    $\begingroup$ In the first video where they drop a block of ice in a deep hole is not just due to the nature of ice because as a kid I remember dropping stones through open borewell and got the exact same noise! $\endgroup$ – Tushar Sharma Mar 6 '20 at 7:45
  • $\begingroup$ I have heard similar noises when sliding sideways with cross-country skiis. They have a metal rim. $\endgroup$ – Davidmh Mar 6 '20 at 8:45
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    $\begingroup$ Essentially a duplicate of Slinky reverb: the origin of the iconic Star Wars blaster sound $\endgroup$ – Emilio Pisanty Mar 6 '20 at 15:53

The pitch of the sounds start high and end up low. Is this some kind of doppler effect?

No. This is chirp induced by dispersion, which is the acoustic version of the same phenomenon for light. This refers to the fact that, generically, sound waves of different frequencies travel at different speeds.

This can be caused by the material properties of the medium, and it can also occur if the sound wave is confined in some kind of waveguide (like a hole or a sheet of ice). For each individual sample a full analysis is necessary to understand which bit of the circumstances caused the dispersion (so it's hard-to-impossible to tell you any specifics about the individual recordings you've given) but the phenomenon is fairly generic so it really doesn't matter much.

If you have short, sharp sounds, the waveform will typically have a very high harmonic content, i.e., if you decompose it as a superposition of monochromatic waves at different frequencies, it will cover a broad band of such frequencies. For the sounds you've given, the higher frequencies travel faster, and you get that descending chirp as the sound transitions to the lower frequencies which take longer to arrive.

The reason this sounds so similar to a sci-fi 'blaster' sound is because this is how blaster sounds were first recorded: Star Wars sound engineer Ben Burtt created (recorded) that sound by recording the guy wire of a tower when he tapped it with a spanner:

Image source

Under tension, the transverse waves have exactly the same dispersion as the ice, so the physics is the same, and the sound is the same.

For more discussion of this, see this previous question on this site.

It's also worth mentioning that the equivalent phenomenon for light ─ taking a short pulse and passing it through a dispersive element so that the higher and lower frequencies arrive at different times ─ is the heart of what makes Chirped-Pulse Amplification (the dominant technology for creating intense pulses of light) work.

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    $\begingroup$ White light makes the most colorful rainbows. White noise makes the best pew pew. $\endgroup$ – Steve Mar 6 '20 at 23:11
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    $\begingroup$ it looks like he tapped it with a wrench to me. :-> $\endgroup$ – Michael Mar 7 '20 at 7:29
  • $\begingroup$ Or, to firm up exactly how this is connected to the situation at hand, it's that the hard smacks of the fast-falling piece of ice against the walls of the long, deep hole are being distorted and modified by this dispersion effect so that they sound quite different upon reaching the listener's ear (or the camera's microphone, as it may be). $\endgroup$ – The_Sympathizer Mar 7 '20 at 12:39
  • $\begingroup$ Also, while I wasn't able to find the original video I'd seen that came to mind, here's a youtube clip of an analogous drop being done with a concrete-walled hole: youtube.com/watch?v=7qETKlMuGt8 $\endgroup$ – The_Sympathizer Mar 7 '20 at 12:41
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    $\begingroup$ You can see two contrasting situations in the nordic skating video. In one of the shots where the cameraman skates beside the skater, you cannot hear any chirping sounds; just the original ice cracking noises (youtu.be/v3O9vNi-dkA?t=123) But in all the wide shots and aerial shots, the component of sound travelling through the ice reaches you first, and you can hear the chirping. (youtu.be/v3O9vNi-dkA?t=148) $\endgroup$ – AlphaLife Mar 7 '20 at 14:12

This phenomenon is known as Acoustic Dispersion.

Acoustic dispersion is the phenomenon of a sound wave separating into its component frequencies as it passes through a material.

This happens because the phase velocity of a sound wave is a function of frequency in a dispersive media $^{\dagger}$. Much similar to how electromagnetic waves disperse when they pass through prism.

Sound waves consist of waves of many different frequencies. When a sound wave travels through air, its component frequencies usually travel together at the same rate, so they all reach the human ear more or less simultaneously. But due to ice being a dispersive media the sound waves propagating through it disperse. Hence high pitch frequencies get separated from low pitched one. And this gives that sci-fi effect to the sound that you hear.

This has been explained over here:



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