Acoustic interference (flying over our heads) 

The sound at 8:00 that demonstrates the Doppler effect isn't from the plane's engines -- it's the same effect as blowing across the top of a bottle and making a sound. It only happens at low altitudes because it's speed dependent and jets of that size at low altitudes are moving slowly because they're either just taking off or about to land. On the Airbus A320 series of planes, it's the holes in the wing that allow air into and out of the fuel tanks as the outside air pressure changes, and the sound can be lessened by disrupting the air flow over the opening. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-IIk7sR3DzzQ.html

I can't wait for the next plane to fly over so I can do the squats!

This is a great video! I would totally have answered "the doppler effect duh" if asked about this phenomenon before

Damn I love this video. My high school was right under the take-off route of a nearby airport, and I finally know why the sound of planes flyinng over would change when we switched seats in the classroom! A question that has been haunting me for more than a decade finally got answered!

The doppler-effect that you're hearing is from a the howl of the the turbine or compressor, which is a constant tone, rather than the nearly white noise of the efflux coming out the rear of the engine. The white noise gets the delay "resonance", because it is composed of nearly every frequency, while the howl is hardly affected, because it's a pure tone.

I used to sit on a rocking chair near a river and every time the rocking would create this going up and down of the frequency. I toyed with it and got the feeling this was weird, because the sound didn't revert to normal when I stopped moving, it depended on my position. Now I understand why. Thanks!

The spectrogram at 8:09 is SO COOL! Also casually discovering this phenomenon in your daily life rather than is just a massive flex. Well done and congrats on following your curiosity to investigate this! This is a very well produced video, I'm very glad I clicked on this. The broadband noise might be due to mixing of air turbulence behind the aircraft en.wikipedia.org/wiki/Jet_noise while the tone that you can hear/see a Doppler effect of might match the engine RPM (I would be surprised if it doesn't, and would love to know what else might it be.)

Aka comb filter. very well made video on this topic. Haven't heard anyone talk about the evennes and oddnes of it. You can then think about this phenomena with regards to waveforms, Sawtooth and squarewave then become quite interesting.

The quality of this video is on par with many much bigger channels, and it teaches a thing I had no idea about despite having been watching sci-pop for years. The graphical aspect is superb, exactly what is needed to explain such a complex topic. Amazing job!

8:00 i can hear both phenomena there! Wow that's awesome! Thank you sir for this video.

5:15 An experiment that anyone following can do is to blow at finger keeping it in front of face and listen to the reflected noise - it changes in corelation to distance, not to the velocity of the finger. Regarding overall topic of the video: very cool observation and clever explanation! I was intrigued by 3Blue1Brown video regarding SoME2, but not spoiled with the explanation - tried to think about it by myself and did not figure it out :)

I've been baffled by this effect for the past 20 years of my life. Amazing to run across this excellent explanation by random chance today!

The Doppler effect is still there. But as you're analysing not a tone but white noise with equal frequency distribution it does not matter. Frequency shifting of white noise is still white noise.

If you use "white" light for the double slit you will see a rainbow pattern (similar to a prism). This is actually used in scientific for spectral analysis. Search for "diffraction grating" if you are interested.

Really interesting! I have always thought Doppler as well. in music production /sound design this effect is called comb filtering.

Thanks for creating and sharing this great video. This is one of the most interesting things I've learned recently.

Outstanding description of this fascinating effect. Thank you!

I was searching an explanation about plane sounds for months, thanks for making this video!, learned a lot.

I've been wondering about this for years after moving to a house under a popular high-altitude flight path; this video was so well done explaining the phenomenon while also fostering an interest in science. Thank you very much for making this!

Thanks! This was an amazing description of the phenomena and the cause. Please make lots more videos!

Awesome video, the recap at the end feels especially good, you are a good teacher 🙌

Very good explanation and presentation of a phenomenon we’ve all experienced but probably never thought about why it appears this way.

Great observation and amazing explanation ! Looking forward for more videos by you.

This question caught me some days ago when I was standing on my terrace and a plane went by above me. I thought, "If this is the good old doppler effect, than why is the pitch increasing as the plane is going past me?" I didn't put much effort into actually thinking about it but you did it for me. Thanks alot for this well put and intuitive explanation.

Very interesting, it's not unlike 'sample delay' used in audio engineering - and in fact this gives me some ideas to manipulate it in some interesting ways. Thanks!

Great graphical representations man. Well done. Subbed.

This feels like a 2blue1brown vid Keep up the good work!

I've wondered about this for so long! It's one of those things that just get shrugged off if you bring it up in a conversation, so I never made the connection. I did see an application for it, a flashlight for the blind. By having a handheld white noise generator that emits in one direction, you could reveal portions of a whole room. Tested it a bit myself, even though I have no training in echolocation I could easily get around a pitch black room and tell if something was there and how far, even the density of it, like cloth vs metal, and it worked better than clicking since it gave you a constant awareness. With a bit of practice, we were able to play catch in a totally dark room, granted the ball had to be something like a beach ball to reflect enough sound

🎉 I figured this out when I was a kid - took a while but I got the same answer. There is another effect which is equally baffling to start with related to a slatted fence by a road - when a car goes by it can produce a tone due to multiple reflections from each slat - all good fun for the whole family.

Awesome work, I understood both things (doppler and echo) in a practical and entertaining way.

Super interesting and incredible production value!

Living in a very quiet house with only a few white noise sources, I can sympathize with the author, who discovered this while walking past an AC unit. I always figured "ok it is weird reflections (from the shape of the room?)", but this is way more detailed and useful! It is indeed "weird reflections" but based on angle and distance! Very cool video, thank you!

With regard to the distinguishable sounds that do show the doppler effect: jet engines produce sounds with specific pitches from their rotating components - the compressor, fan, and turbine. It is particularly noticeable with low-bypass engines, now only found on high-performance military aircraft, together with a few '60s and '70s airliners and business jets (in those places where they are allowed.) Specific pitches can also be generated by the airflow over the airplane, and particularly when slotted flaps are deployed. Perhaps this accounts for your perception that it is most noticeable with lower-flying aircraft, as the flaps are deployed for takeoff and landing? Another possible explanation lies in the fact that high-pitched sounds are attenuated more strongly than lower ones. This would only hold up if, when listening to a high-flying airplane, almost all of the sound one hears is lower in pitch than the distinct sounds that show the doppler effect. This is an excellent video - science exposition as it should be done, with observation, hypothesis and verification following one from the other in the right order!

that's an incredible video. ngl, i'm here because of 3b1b, but that video has been in my recommended for some time, so it looks like you're on good terms with youtube gods. wish you luck and channel growth.

Subbed. Great video, I always noticed this but never bothered to know the why. Thanks for making this video.

incredible video, never would've thought it was just reflected sound

EXCELLENT - thank you. Always wondered why the frequency goes up as plane goes away.

Nice, really good explanation of something not often thought of.

I've heard the Doppler effect as a jet passes overhead, but never noticed that- yeah, wow- there is a frequency component that rises after the aircraft has passed. 3blue1brown called attention to this (by referring to this very video) and I was really blown away by listening closely to the sounds. I still hear the dominant sound of the decreasing frequency, but thanks to you I also became aware of the rising frequency. Very cool, and thank you for the explanation!

awesome video, I loved the editing and explanation

Absolutely brilliant video.

Неплохо. Помню на лабах по физике часто подобные качественные вопросы нужно было разобрать, чтобы сдать.

Excellent explanation and illustration!

Wow. Really excellent. This should be an intro to audio recording. Miking and mixing are almost perfect extensions from here.

My hat off to you, sir. Wonderful.

Beautiful animations!

Amazing explanation! You deserve more subs.

Omfg I've been looking for what this phenomenon is and this video finally answered it! I could recreate it with a comb filter/phaser but I never knew why this happens in real life :D

Thank you, this was refreshingly interesting.

the Berdnikov effect

Super! Excellent graphics as well.

This is what the Flanger effect does. You can hear it when you "shhh" near a wall and slowly move toward and away from it. You know that you do not change the sound you are making, but you change the distance to the wall, while your distance to the floor remains unchanged. You hear exactly the same effect when moving. If you stand still, the perceived pitch will not change.

Very interesting explanation!

So, I suppose the summary should be something akin to Forrest Gump's famous line at Jenny's gave - "Maybe it's both. Maybe both is happening at the same time" 😉 Отличное видео с Саша! Спасибо и привет из Австралии!

It’s always crazy to me how common comb filtering really is in the real world, it’s so often used as an extreme effect in produced music but is really just nature at work.

Brilliant. Loved every second.

Great explanation, learned something new

This is great information! What I had noticed is that I don’t hear a plane coming until it’s a certain “height” away from me, and I found that strange that it’s not a gradual increase starting as soon as it’s above the horizon. I’m sure there something related here, in that the echo doesn’t happen at low angles.

Such a fantastic explanation!

Great video, and great explanation!

Very nice explanation. Great video!

Wow. Nice explanation by way of illustration.

Excellent explanation.

The law of resonance could help us safer operations....thank you for this side way presentation...I was really nonverbal learner until now

Very interesting video, never thought about this before.. thanks =)

Fascinating, thanks!

The sound of distant thunder also produces the effect of pitch dropping. First you hear high frequencies and the pitch drops as the volume increases. I've thought about that quite a bit and have no explanation.

Really interesting, thank you

Great video, thanks

Wow! This is so interesting

Good old comb filter effects

Excellent!

I'm just amazed at how small an echo can be perceived by the human ear. 😳

The gradients of temperature and pressure change the speed of sound by altitude, and the sound waves are bent toward the side of lower speed. One result is that it's hard to hear the noise of an airplane on the ground from a distance away, but the loudness increases sharply as the plane takes off.

interestingly enough there's a guitar effect that is called flanging that is often said to sound like an airplane and it works with a similar logic: adding a very slightly delayed version of the signal to the signal itself while slowly changing the delay time. nice.

Sounds like the flange effect on guitars. I’m sure it’s produced using sine wave interference in a circuit. Awesome.

GENIUS!

Very interesting! It may solve why when I hear jets fly near where I live sounds really weird, like you don't hear anything then suddenly you hear a rapid descending white noise, then normal plane flying noise, then the pitch rises sharply and is then cut off.

I just experienced a puzzling pitch shift from an AC unit (as I walked past) and RU-vid recommended this video.

Great video!

this is awesome wow

super cool thanks man

Very well observed!

Very cool video!

You’ve just explained the barber pole filtering / phasing effect well known by musicians and well described by mathematicians. Yes, it’s based on variable length delay and mixing direct signal with delayed.

interestingly enough there's a guitar effect that is called flanging that is often said to sound like an airplane and it works with a similar logic: adding a very slightly delayed version of the signal to the signal itself. nice.

Oh no. I would have thought it's Doppler, too. This experiment proves I need to be a bit more sceptical about the world sometimes

I love it

god i was trying to find this video a couple months ago thank god i found it

There is also the differences between the frequencies emitted by the front of the reactors and the back of the reactors. This is most distinctive with war planes flying with afterburners engage.

10/10 very good video!

well explained👍👍👍👍👍

A plane flew over as I watched this video, and I wanted to run outside and lay on the ground

omg, great video

The sympathetic vibrations of the sheet metal that make up the underside of the wings mostly occur in the lower frequency range. This sound is mostly directed at right-angles to the surface of the metal. I think this is contributing to the effect, if not dominating it. (Lay down on the ground to see if the effect persists, to verify.)

Very cool!

To anyone who has spent time with guitar pedals or synthesizers, it's clearly the phenomenon described as Flanging. Which is very different from the dopler effect which is solely concerned with a pitch shifting, not with interference patterns like this.

Helicopter flew over my appartment right at the end of this video, good thing i was inside, i would have looked like a fool if i was outside rn.

that's extremely cool

Pretty cool!