Acoustic interference (flying over our heads)

[@davidlynch5748]

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. kzbin.info/www/bejne/f3rOaKaIaKmtsLM

[@v44n7]

damn thats so cool, thanks for sharing. Also Alek amazing video!

[@fredoverflow]

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

[@aleksandrberdnikov2439]

As I mentioned, you can employ somebody to be a plane for you in that respect:)

[@potato733]

I produced the "shshshshshsh" white noise with my mouth and went closer and farther to the wall 😂

[@MadScientist267]

Jets everywhere here... Definitely gonna check this out

[@v44n7]

@@aleksandrberdnikov2439 i am curious if you do the same but with your hand to any sound. Depending on which direction are facing you hand with you ear

[@aleksandrberdnikov2439]

@@v44n7 You can do that and hear a change, but it's much less clear than with a solid wall or floor.

[@DrTrefor]

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

[@aleksandrberdnikov2439]

So would've I, for the most of my life:)

[@explodingonc2782]

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!

[@aleksandrberdnikov2439]

That's really cool that you've noticed it for a puzzle that it is! Making this video let me realize how many more situations I've witnessed this effect in (like the one you described, say), yet it never occurred to me to see there a question in need of an answer. On the other hand, it became a bit annoying taking a note of it every damn time, can't unhear it now:D

[@RigoVids]

Same! Although not a decade.

[@JohnDoe-fk6id]

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.

[@FlyNAA]

I wouldn't be Kramer-ing in to random internet discussions with this, but since we're picking apart geeky details... the front part is called the compressor, or fan, but not turbine. That's the part in the back.

[@JohnDoe-fk6id]

@@FlyNAA which is why I mentioned both. Depending on the engine design, the majority of the howl can come from either one.

[@FlyNAA]

@@JohnDoe-fk6id ah - I misread you

[@realityassembly7368]

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.

[@germaindesloges5862]

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!

[@diggoran]

pretty safe to assume your rocking chair was next to a wall, and the wall was creating the reflection?

[@oceannuclear]

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.)

[@megamaser]

I would expect it to be the number of fan blades multiplied by the revolution frequency, since each blade should produce at least one peak and trough. There would probably be harmonics, and a lot of interference with waves from adjacent blades

[@DiveTheseClips]

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!

[@michaelhanford8139]

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

[@knurlgnar24]

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!

[@kabotteam]

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 :)

[@Waffles_Syrup]

that's probably more because the velocity of the air changes with the inverse square law

[@user-nq6kh1ke4e]

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.

[@aleksandrberdnikov2439]

I enjoy using CD this way to watch the solar spectrum. There is something mesmerizing in its pure pattern of fine lines:)

[@itsmealec]

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

[@Graydon9]

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!

[@rkalle66]

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.

[@TheMasterKillerify]

the Berdnikov effect

[@daveozip4326]

🎉 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.

[@liamquinn]

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

[@pluspiping]

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!

[@aleksandrberdnikov2439]

Yeah, in a closed room it becomes more complicated with multiple reflections and complex geometry. For example, it is fun sometimes to walk around the kitchen and nearby, and hear how in some places the hum of a fridge or microwave (or youself:) is much quieter than in others, so you can kind of plot out Chladni patterns on the volume of your home

[@raico6890]

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

[@steviewonder9209]

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!

[@aleksandrberdnikov2439]

I'm really glad to hear it, getting others to share the "aha!" moments in understanding the nature is really satisfying:)

[@harmonicresonanceproject]

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!

[@zenithparsec]

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

[@Shawak9]

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.

[@BillySugger1965]

Outstanding description of this fascinating effect. Thank you!

[@colinratcliffe3074]

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

[@skeptiks]

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

[@error200http]

2girls1brown

[@weylinstoeppelmann9858]

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

[@aleksandrberdnikov2439]

Is there something with this "acoustic lantern" that I can google? I knew about the clicking trick, but what you describe seems much more noob-friendly) Will try with a phone I guess...

[@vladimirstarostenkov4417]

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

[@aleksandrberdnikov2439]

Эх, у нас в школе хоть с теорией было хорошо, практики/лаб содержательных не припомню. Интересно стало; а можете примеры привести?

[@vladimirstarostenkov4417]

@@aleksandrberdnikov2439 одну задачку из школы помню. Существует способ измерения силы поверхностного натяжения методом отрыва кольца. Так вот, демонстрируется такая установка, измеряется поверхностное натяжение воды, которое сходится в пределах погрешности метода с табличным значением. Далее в воду помещается анод, а снаружи сосуда - катод, подается напряжение и сила поверхностного натяжения меняется. Далее следует предложение объяснить почему "у воды под действием электрического поля изменяется коэффициент поверхностного натяжения". Злая шутка кроется в чистоте эксперимента: кольцо металлическое и, будучи подвешено на металлической проволоке к прибору, является проводником погруженным в воду, в которой начинается незаметный невооруженному взгляду электролиз :) Еще вопрос вполне доступный школьнику-физику - это про "очки с дырочками", темные такие очки с непрозрачными стеклами, в которых насверлено много дырок по 1-2 мм в диаметре - просто объяснить принцип их работы. Остальное уже в универе у меня было.

[@tolkienfan1972]

A country that actually teaches their children math and physics. Wish the US did

[@A.Raybould]

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!

[@petervanderwaart1138]

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.

[@micmac8171]

This works if the plane is high enough and not too far. Otherwise unequal spectrum ahead and back from the turbo engine comes into play.

[@aleksandrberdnikov2439]

How so? The delay is only worth of few meters for sound, about a meter for a plane. I don't see how that would make a significant difference in direct and echoed sound. Or you're saying that on approach we hear the front, on retreat we hear the back, and that is also a factor? I guess, but the moving pattern is still there, just on a different background...

[@micmac8171]

@@aleksandrberdnikov2439 Yes, the front and rear sounds of a tubine are vastly different. I have been a lot on the airfield with jets and know how much the angle to the turbine matters.

[@swancrunch]

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.

[@erikziak1249]

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.

[@ThompYT]

That's what the video says

[@osoreru4381]

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

[@senorjp21]

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.

[@TG-to5nf]

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

[@veyrondarren1064]

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

[@mjears]

Excellent explanation and illustration!

[@christophermadsen340]

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

[@techdoc99]

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

[@kharybdis]

Absolutely brilliant video.

[@gyur6]

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

[@johnjoyce]

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

[@crowlsyong]

Great graphical representations man. Well done. Subbed.

[@EPMTUNES]

Super interesting and incredible production value!

[@jontime59]

My hat off to you, sir. Wonderful.

[@tripham9422]

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

[@jlchappell]

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.

[@joyphobic]

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

[@mihalyponyiczki1855]

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.

[@Airatgl]

Very interesting explanation!

[@silverXnoise]

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

[@solidSchmaltz]

Beautiful animations!

[@mykeprior3436]

Excellent explanation.

[@Xenro66]

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

[@JohnChampagne]

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.)

[@aleksandrberdnikov2439]

Even if there is a contribution from such effect, it's not the stripy pattern that kinda dominates the spectrogramm. I've checked what you suggested, and couldn't hear the pitch going back up, only the Doppler lowering; so - no, I don't think so.

[@darkelwin02]

Good old comb filter effects

[@antonniedersteiner4377]

Super! Excellent graphics as well.

[@codyexzonk]

10/10 very good video!

[@Googahgee]

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.

[@mihalyponyiczki1855]

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.

[@ed.puckett]

Thank you, this was refreshingly interesting.

[@NonBinary_Star]

Such a fantastic explanation!

[@therealchayd]

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.

[@cyndicorinne]

Wow. Nice explanation by way of illustration.

[@mytech6779]

This assumes you are on a hard flat surface. Standing in a tall hay field is likely to drop the amplitude of the reflection substantially and allow the doppler effect to dominate.

[@The0ldg0at]

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.

[@hanselpedia]

Great explanation, learned something new

[@Mr0neShotAway]

Really interesting, thank you

[@Beatsbasteln]

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

[@seedmole]

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.

[@PilotPlater]

Fascinating, thanks!

[@vintyprod]

Brilliant. Loved every second.

[@sickboi11111]

Great video, thanks

[@Scar32]

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

[@beefchicken]

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

[@Kezenmacher]

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

[@louiscallens4183]

Very nice explanation. Great video!

[@svenb4475]

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.

[@JimGriffOne]

Comb filtering. Reflections from the ground interfering with the direct sound.

[@NoahSpurrier]

Some of the effect may be due to change in the levels of air density the sound moves through.

[@pavelperina7629]

Interesting. I'll try to look at spectrum of sound of low flying Jas-39 Gripen. It makes almost starwars-like sound of passing spaceship (but inconveniently loud). I guess it's combination of intake compressor/fan noise, this effect, doppler effect and simply moving at 700km/h at 200m altitude or so. But interestingly L-159 Alca which uses the same training corridor sounds different.

[@ahhuhtal]

Sometimes you can hear the sound of a plane start very abruptly. Often so that different frequency components of the sound start at a slightly different time. I've been wondering about what causes that. I've been guessing at some type of total internal reflection type thing occurring between air layers obscuring the sound initially, and then suddenly allowing the sound to pass when the geometry changes as the plane moves. If you know something of this, I'd love to hear about it :-)

[@compfox]

Do you mean the "miiiiuuuuu" sound, when a plane is approaching ? I'm wondering abouth this for a long time too. I think some aspect is the planes velocity in relation to the speed of its sound. When the plane travels faster than sound, this noise gets compressed to a supersonic "boom".

[@ahhuhtal]

@@compfox I'm not sure if that's what I mean 😀. What I'm talking about is when the sound of a plane is first barely audible, but suddenly becomes louder. If I recall correctly, the sound starts from the high frequency end, and extends toward the lower frequencies. This takes about a second.

[@compfox]

​@@ahhuhtal Yes. Thats what I have in mind. As a child, not knowing many about turbine engines, I guessed the plane was something like "putting the brakes on" aproaching the nearby airport.😆 ​ @Antti Huhtala Yes. Thats what I have in mind. As a child, not knowing many about turbine engines, I guessed the plane was something like "putting the brakes on" aproaching the nearby airport.😆 ​ @Antti Huhtala Yes. Thats what I have in mind. As a child, not knowing many about turbine engines, I guessed the plane was something like "putting the brakes on" aproaching the nearby airport.😆 ​ @Antti Huhtala Yes. Thats what I have in mind. As a child, not knowing many about turbine engines, I guessed the plane was something like "putting the brakes on" aproaching the nearby airport.😆 ​ @Antti Huhtala Yes. Thats what I have in mind. As a child, not knowing many about turbine engines, I guessed the plane was something like "putting the brakes on" aproaching the nearby airport.😆

[@koenth2359]

Very well observed!

[@rpocc]

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.

[@lfz1nho]

awesome video, I loved the editing and explanation

[@zachreyhelmberger894]

There is another weird sound effect I hear sometimes. If a plane is coming in for landing approach, you will sometimes hear this weird downward drop in frequency over one to two seconds. I thought maybe it was the engines throttling down suddenly but now I'm not so sure..

[@spacemanmat]

Please place the recording device on the ground so we can isolate the Doppler effect.

[@ThingEngineer]

Amazing explanation! You deserve more subs.

[@HelPfeffer]

Wow! This is so interesting

[@theinspector1023]

Excellent!

[@gokulchandran5586]

well explained👍👍👍👍👍

[@danielchin1259]

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

[@aleksandrberdnikov2439]

A way to develop techno-paranoia :)

[@hlibprishchepov322]

Wow it might be interesting to make app which gives info about plane using sound

[@DustinGunnells]

GENIUS!

[@playgroundchooser]

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

[@aleksandrberdnikov2439]

Well, it's not about the human ear, it's not like the echo here is more elusive than the original sound.

[@Beakerbite]

The echo is not much quieter than the source sound. Ground is hard, and especially on concrete, pretty flat. So distortion is minimal. The main reason why echoes you're used to are quiet is due to the inverse square law combined with echoes originating from a distance source, which saps the echo of it's energy. With the echo source being only your height away, it's very close and thus hasn't spread out very far.

[@yoonseongdo3303]

this is awesome wow

[@bbrazen]

Great video!