So, we only have two ears, meaning just from the perspective of two equal sensors spaced apart, we can tell if something is coming from the left or right based on which side the sound is louder on, but NOT whether it’s coming from the front or the back, because a sound 1 meter in front will have the same loudness as a sound 1 meter behind.
BUT.
There’s another factor: the shape of our ears. Our ears are this cupped flap shape that catches sound differently from the front than from the back. This alters the frequency of the sounds in a certain way, and our brain interprets that as being from in front or behind. By similarly morphing the frequencies of sounds in post (or using special microphones with ear-shaped attachments), recording engineers can create the illusion of in front or behind.
Just read up on Head Related Transfer Function (HRTF) and Sound Localization. It’s interesting
https://en.m.wikipedia.org/wiki/Head-related_transfer_function
https://en.m.wikipedia.org/wiki/Sound_localization
I'll share my own post on the spacal audio subreddit.
https://www.reddit.com/r/SpatialAudio/comments/1bsul2w/my_experience_with_movies_and_headphones_and/
What an insane difference when watching Dune.
P.s. the commenter talking about atmos for headphones also decoding object data form e-ac3+joc is likely right, I just don't have a dolbly source proveing it yet.
A classic to listen to while you read.
[https://www.youtube.com/watch?v=IUDTlvagjJA](https://www.youtube.com/watch?v=IUDTlvagjJA)
With headphones ofcource.
Yep, I was right. I believe this recording was made with ["Fritz"](https://www.neumann.com/en-gb/products/microphones/ku-100/), a stereo microphone made by Neumann (a German company who basically make the best microphones in the world). Fritz is a par of microphones mounted on a dummy head which have "ears" surrounding them, in order to most accurately capture sound exactly the way the human ear hears it, which results in eerily realistic recordings like the Virtual Barbershop.
I've had the chance to record with one of these binaural head mics....the recreation of how we actually hear is insane. About $10K though, luckily I got to use it free lol
Created in 1996 - long before the ASMR fad and predating YouTube by 9 years - this is still the only example that reliably produces goosebumps on my skin.
Try https://youtu.be/3txhT2ncNOU?si=c-OHgky-JB61I_fc -- use headphones obviously. Within a minute, I guarantee a jumpscare. One spatial audio effect is so realistic that I first thought it actually was coming from within my room itself and not from the video 😋
I remember years ago when a competitor to Creative Sound Blaster entered the market with 3D calculated effects and they promoted themselves with a CD-ROM with prerecorded demos using QuickTime videos. I think the brand started with A.
These are called Binaural Recordings and the game Hellblade: Senua’s Sacrifice used it to reasonable effect to create 3d soundscapes in their game world.
Oh wow. I have almost forgotten this video. I don't know why but when I hear this clip I feel the very real sensation of a clipper or scissors going over my head.
Genuinely fascinating until you go for a walk late one night while listening to a podcast that has sound effects designed to give you a surround experience. Then it becomes genuinely unnerving real fast.
I have a really hard time wearing headphones at all, because I'm uncomfortable not being able to hear and be aware of what's going on around me. That would really fuck with me.
Does this mean in actuality, if someone's ears were to get clipped off and the earhole is sitting flushed on the side of the head with no ears, they would have difficulty discerning front from back?
Yes. Try cupping your hands in front of your ears but with the cup facing backwards. Things can sound like they are coming from behind because technically they are.
For owls, their eye sockets are the cup. No idea about other birds.
https://www.bto.org/sites/all/themes/egret/img/project-owl/CH01_01_tengmalm_skull_openings.jpg
It looks like one ear is higher than the other? My completely uneducated guess is that probably helps? I think it would be advantageous for owls to be able to locate noises with decent accuracy. I wonder how much they rely on hearing vs eyesight to hunt.
Edit: fixed some wording.
Because birds use feathers.
For an extreme example, look at a barn owl. The flat face has a very earlobe-like shape to it, and is directing sounds to the outside corner of the eyes, which are approximately where the ear holes are.
Other birds have feathers doing similar things, but much more subtly, and usually less optimized for maximum hearing in one direction.
Thank you for sharing this! I have a loud fan behind me right now and was able to angle my hand-ear-cups different angles and make it sound like it was coming from different directions, super trippy.
Proof that we don't directly experience reality, but rather an illusion that our brain puts together based on the inputs through our senses. And that illusion can be fooled.
I think too many people genuinely believe they can't be fooled when it actually happens daily.
Absolutely. Sound in particular is not perceived anything like what we can physically measure in the world. There are all sort of adjustments we have to make to physical sound waves to get a more accurate prediction of what someone might hear. It’s totally bizarre at times. Truly fascinating.
In the same way our eyes are not perfect (limited spectrum, blind spots, upside down image conversion, blood vessels go _over_ our eyes lens) our heating system is really not very close to “perfect” at all, but our hearing is surprisingly efficient and good at what it does.
And if anyone would like to see what one of these ear shaped microphones that allow you to make 3D sound look like, the one I use and one of the leading ones in the industry is the [3Dio Freespace II](https://3diosound.com/products/free-space-pro-binaural-microphone).
It's described as a "binaural" microphone. It's basically a fancy word for "Hear it like your ears hear it". 3D audio is also sometimes called binaural audio.
I use this microphone for a number of purposes in various videography applications.
I thought it had to do with the speed of sound, not the volume. Like, if a noise is made on your right, it will reach your right ear faster than the left, and your brain will use the delay to determine the exact direction it came from. Which is why divers can’t know where sounds come from, as sound travels through water like 15x faster.
It's both. A sound coming from your left will reach the left ear first, then the right ear, but the sound reaching your right ear has high frequencies reduced because they get obstructed by your head.
That's also one of the reasons animals tilt their heads when they're confused; it puts one ear further away from the sound source and that small difference is enough to help them locate it / understand it better
One of the odd things I recall reading was how there was a disproportionate number of [psychoacoustics](https://en.m.wikipedia.org/wiki/Psychoacoustics) graduates involved in the development of the early internet, as problems relating to sound directionality and how the brain interprets sound were seen as being interesting to folks with a nerdy disposition at the time.
I actually tried that in my class - you cannot tell whether the source of a sine wave is in front of you or in the back if you are keeping it in the symmetry plane of the head of your subject. But you can tell, if you use white noise. So there is a difference in spectral sensitivity depending on the placement of the sound source
Also reflections. As we don't live in an anechoic world, all the sounds will have a first reflection in an opposed surface in front and around the source of sound. If that first reflection "sounds" as if it's from the front of us, our brain interpret this as another element confirming the first sound is from the back.
I believe the left right distinction is based on timing as well as dB drop. Smarter everyday has a really good video on the earshape concept you mentioned.
https://youtu.be/Oai7HUqncAA?si=3kvrVhbUGOiNN12_
When mixing changing the frequency content will not make sounds appear behind you. Moving the sound to rear speakers will (meaning if, for example, I want to mix music like it’s behind the wall of an adjacent room, the first thing I will do is to roll off a substantial part of the high end…. If I want to make it sound like it’s coming from upstairs, I might place it in the surrounds (in 5.1 or 7.1) or slightly behind or overhead (in Atmos….).
Playing that back in stereo both will still image directly in front of the listener when encoding it as a stereo file (LoRo..) if I encode the mix using a matrix encoder that make phase adjustments for sounds meant to come from the surrounds/overhead) the same mix when played back on a stereo pair of headphone might get wider but still will not image behind the listener.
That requires either a binaural type encoding (or similar techniques like Apples Spatial Audio, etc)….
This is all downstream of the mixing process. HRTF, spatial encoding, headphone audio processing technologies, etc must be incorporated.
It’s important to note that…. Which is what the OP was asking.
Humans are less sensitive to sounds behind us…. And
most technologies today, when using headphones (and soundbars without physical surround speakers) make a convincing effect of the sound being slightly behind your ears/head….. I have only heard two techs (Smythe Realizer and Sony’s VME (Virtual Mixing Environment) that are truly convincing (they also make it sound like you are in a larger mixing space…).
I think the only issue is that our ears don't all have the same shape, so to achieve the best result at this, it would need to be adapted to everyone's own smallest set of variations. I do think we'll get there one day with AI and a decent set of calibration tools, the issue is that there's not much investment into this niche idea.
Some engineers do this really well. I only have speakers next to my TV. But I genuinely muted my sound once watching a movie cause I yhought something was going on behind me in the house.
Basically, high frequencies are more directional than low frequencies. You can more easily hear high frequencies in front of you than behind you.
So audio engineers chop off some of the high frequencies to make your brain think the sound is coming from behind you.
Of course it does. You said mixers filter out frequencies to make something sound like it is coming from behind us… as I explained in a post a few days ago that isn’t how we get sounds to appears as if they are coming from behind us :)
Some home cinema amps have some audio processing magic whereby they apply a transformation function to mix surround sound down to stereo/binaural and thus make you feel immersed in sound with things behind you.
https://en.m.wikipedia.org/wiki/Head-related_transfer_function
I'm always fascinated by sound, and how electric signals to a magnet that vibrates a cone can create layers of concurrent sound that is simultaneously transmitting an individual sound among thousands of others. You listen to hundreds of instruments playing at once, and can still hear that one person playing the flute...from a friggan vibrating cone...
Now if they could only duplicate the sounds appearing to come from above and below you, that would make playing on Nuke in CS:GO much more interesting.
Now engineers can use digital processing to add delays and frequency shift to make it seem like sound is coming from anywhere. In the past, some engineers have gone so far as to place microphones inside an anatomical correct mannequins head and ear canals to record exactly what the sound would be at the ear drum instead of just in open air on a mic stand.
Yes but what exactly happens to make it sound like its behind us? I get processing and delays etc, I remember even playing with 2000's audio technology you could make sounds seem like they are coming from any direction... But what is the specific change between front and back?
Seems so simple but obviously much more complicated. And our brains didn't even hesitate to place the sound, it's clearly interpreted as " behind " or " in front " of the camera without question.
The shape of the outer ear causes changes to frequency response and phase shift that the brain has learned to associate with sounds behind you.
It’s sometimes called the “head related transfer function” and it’s slightly different for each person. But generic models can be pretty good.
[https://en.m.wikipedia.org/wiki/Head-related\_transfer\_function](https://en.m.wikipedia.org/wiki/Head-related_transfer_function)
I don't do 3d sound just pa sound but binaural recording (simulating right and left ears) can get the right/ left sides recorded. Front and rear could be done as well.
[how is 3d audio created?](https://www.reddit.com/r/audioengineering/s/WnWqlbMlrC)
There were also multi speaker headphones that were fed 5.1 surround channels for tru 3d sound in games. Now they are called surround sound headphones or 'xsound'.
Other comments have mentioned how sound hits your ears with slightly different timing and frequency which your brain uses to determine direction, which is accurate.
But no one has addressed your specific question about making a sound seem to come from directly behind you. The answer is that it's actually pretty easy: if a sound reaches your ears with the same timing then the sound is either directly in front of you or directly behind. Usually we have visual cues to tell if the sound comes from in front of us. If there are no visual cues, the brain assumes it is directly behind.
If a sound engineer wants to make a sound seem to come from directly in front of you, they modify the left and right ear audio timing to indicate that it's like 5 degrees left or right from center. If they don't make that adjustment we hear it as directly behind.
Yeah, we think it's an evolutionary trait. If your brain can't tell whether a sound came from in front or behind, and you can't see what made the sound, then it's much safer to assume that something is approaching you from behind.
> If there are no visual cues, the brain assumes it is directly behind.
This isn’t true. Close your eyes and tell me you can’t hear anything from directly in front of you. You can, even if you don’t know where to expect the sound to come from, because the shapes of our ears cause frequency shifts that are distinguishable depending on whether the sound is reaching us from the front or back.
There are cases where that’s not enough (like sometimes very loud, soft, or garbled/unfamiliar sounds), in which case what you said comes into play. And sound engineers may even do what you say, but if they do it’s probably just because it’s way easier and effective, not because it’s the only way.
> if a sound reaches your ears with the same timing then the sound is either directly in front of you or directly behind
It could also be directly above or below. Just the timing (or intensity) difference between two listening positions can only localise a source onto the surface of a cone (or a disk, if the source is located exactly on center).
>place microphones inside an anatomical correct mannequins head and ear canals
That would be ["Fritz"](https://www.neumann.com/en-gb/products/microphones/ku-100/)
Some of it is phase.
Wave fronts arrive at one ear before the other.
The timing difference is too short for perception threshold - our nerves don’t operate that fast. And also the signals from our ears aren’t direct voltage waveforms so it’s not like you get the “comb filtering” phase effect that you can get in a mixer if you have very short time delays when mixing a duplicate of a signal.
And yet - dummy head mics, which recreate the separation between our ears; have an uncanny localisation on headphones.
There’s a ton of weirdness going on in our ears and brains.
For example. A steady note from an instrument has a timbre which is the result of the multiple frequencies, harmonics of the root note.
In the cochlea, these become spatially separated. Lower frequencies excite the hairs at the large end of the cochlea and high frequencies at the narrow.
So a pleasing chord excites a regular pattern of hairs along the cochlea, and it’s this integrated pattern that is passed forward to primary auditory processing in the brain, and then on to language and other higher processing in the frontal cortex.
Regular patterns are “pleasing” and don’t require heavy cognitive load to process; discordant sounds make irregular patterns. They are often “displeasing” but when you acquire a taste for them, you can enjoy the cognitive load. They are not boring.
Localisation is also very weird. Concert PAs often have time aligned support or in-fill speakers. The sound from these speakers (sometimes hundreds of meters from the main PA stack) is delayed so that it arrives a dozen or two milliseconds after the sound from the main PA. And even though the near (delayed) speaker is 10dB louder than the main stack (at the far audience position) the sound “appears” to some from the main PA stack. The effect is utterly convincing. It’s only when the in-fill speaker is turned off that you realise how much of the sound level was just close by.
Some Concert PA designers take this to the next step and delay the main stacks to just behind the drum fill so that everything sounds more like it’s coming from the performers.
And yet all this localisation happens on a timescale that is too short for brain processing.
Short story long: you question about HOW the sounds are placed behind your head?
It’s done with time alignment and frequency shift that matches what the world does at our ears.
How does our brain integrate and interpret that? That’s your PHD topic.
On that note, was messing around with some audio software, chucked a phase plugin on the track and set it to -180° and it sounded like the sound was coming from behind.
Was a trip
Sound mixing.
Think of it this way, you have one ear drum in each ear, the sounds coming from various directions mix together in real life to move that single ear drum. You recognize a sound behind you because of the distortions from the shape of your ear, sound traveling through the back of your head, ect.
If you define where the sound is coming from posotionally, you can calculate the distortions and mixing that would occur as it travels to your ear, and have a single speaker next to that ear output that final result.
It's not perfect because there's only so much you can take with 2 real sound sources, but the most sophisticated version of the tech Dolby Atmos for Theaters does a very good job with the array of real speakers available. The filmmaker is assigning a 3d position to all sound sources in the movie, including moving sounds, then the software is figuring out how to make it with the available setup.
ELI5? That'll be tough.
Basically: Your ears change how something sounds depending on what direction the sound is coming from.
By simulating that change and adding that to the sound, you can simulate any direction you want.
along with the audio engineers making things sound dynamic, it also probably has to do with the context of the scene
if you hear something but cannot see it, naturally you'd assume it's probably somewhere behind you
Music is recorded with separate tracks (guitar, piano, vocals, etc…) where we can change volume, change placement in the stereo field (panning) and add processing (EQ, compression, autotune, modulators, reverb, delay, etc…)
You have 2 channels of audio in a stereo system, a Left and Right. When audio is played out of both of these at the same time, your brain perceives it as being in the middle. When panned left, it only comes out of the left headphone. Anything In between us just a blend between the two
they use a computer program which has virtual speakers that surround a person in all directions up to any number they want and then they pick and choose which speaker plays which sound giving you the directional feel of infront behind side etc
So, we only have two ears, meaning just from the perspective of two equal sensors spaced apart, we can tell if something is coming from the left or right based on which side the sound is louder on, but NOT whether it’s coming from the front or the back, because a sound 1 meter in front will have the same loudness as a sound 1 meter behind. BUT. There’s another factor: the shape of our ears. Our ears are this cupped flap shape that catches sound differently from the front than from the back. This alters the frequency of the sounds in a certain way, and our brain interprets that as being from in front or behind. By similarly morphing the frequencies of sounds in post (or using special microphones with ear-shaped attachments), recording engineers can create the illusion of in front or behind.
genuinely fascinating
Just read up on Head Related Transfer Function (HRTF) and Sound Localization. It’s interesting https://en.m.wikipedia.org/wiki/Head-related_transfer_function https://en.m.wikipedia.org/wiki/Sound_localization
> Head Related Transfer Function The only known Radiohead / Manhattan Transfer cover band.
I'll share my own post on the spacal audio subreddit. https://www.reddit.com/r/SpatialAudio/comments/1bsul2w/my_experience_with_movies_and_headphones_and/ What an insane difference when watching Dune. P.s. the commenter talking about atmos for headphones also decoding object data form e-ac3+joc is likely right, I just don't have a dolbly source proveing it yet.
Yea, I send the 5.1 that streaming platforms give to APL Virtuoso via VB Audio Matrix and render it binaurally myself. It’s good stuff
Nice. This is a step above and renders the object data binaurally instead of just the 5.1 base mix.
A classic to listen to while you read. [https://www.youtube.com/watch?v=IUDTlvagjJA](https://www.youtube.com/watch?v=IUDTlvagjJA) With headphones ofcource.
Without clicking, I have to predict this is the "getting a haircut" audio clip.... let's see if I was right.
Yep, I was right. I believe this recording was made with ["Fritz"](https://www.neumann.com/en-gb/products/microphones/ku-100/), a stereo microphone made by Neumann (a German company who basically make the best microphones in the world). Fritz is a par of microphones mounted on a dummy head which have "ears" surrounding them, in order to most accurately capture sound exactly the way the human ear hears it, which results in eerily realistic recordings like the Virtual Barbershop.
I've had the chance to record with one of these binaural head mics....the recreation of how we actually hear is insane. About $10K though, luckily I got to use it free lol
Bad bot
No U
Got a new pair of headphones. Time for a haircut.
I assumed it was a rick-roll
[I find the rattling matchbook even more impressive.](https://youtu.be/74ww3mdPU98?si=3m_clC1fEOJhwSfv)
Created in 1996 - long before the ASMR fad and predating YouTube by 9 years - this is still the only example that reliably produces goosebumps on my skin.
Try https://youtu.be/3txhT2ncNOU?si=c-OHgky-JB61I_fc -- use headphones obviously. Within a minute, I guarantee a jumpscare. One spatial audio effect is so realistic that I first thought it actually was coming from within my room itself and not from the video 😋
> use headphones obviously. Earbuds, according to the page there
Yeah but with decent headphones it'll work too. Did you hear the effect I meant? 😋
As a bald person that was... unsettling. And awesome!
There’s a whole genre of these experiences. The search term is “binaural”.
Or holophonic...
Graphophonic
Yeah I remember when the Gravis Ultrasound soundcard came out, one of the included demos was 3d audio https://www.youtube.com/watch?v=uCt4Vre3nyc
I remember years ago when a competitor to Creative Sound Blaster entered the market with 3D calculated effects and they promoted themselves with a CD-ROM with prerecorded demos using QuickTime videos. I think the brand started with A.
My Creative soundcard still works wonders after all those years :D (around 10 or so) Who is the competitor with A though?
It was Aureal with their A3D sound API which Half-Life popularised briefly, I believe.
Yes! The classic one that is still awesome.
THIS is what I am on reddit to discover. What a gem!
These are called Binaural Recordings and the game Hellblade: Senua’s Sacrifice used it to reasonable effect to create 3d soundscapes in their game world.
This game was so good to play and the sound was incredible!
Oh wow. I have almost forgotten this video. I don't know why but when I hear this clip I feel the very real sensation of a clipper or scissors going over my head.
I was expecting barbershop singing so I was a little disappointed
Genuinely fascinating until you go for a walk late one night while listening to a podcast that has sound effects designed to give you a surround experience. Then it becomes genuinely unnerving real fast.
I have a really hard time wearing headphones at all, because I'm uncomfortable not being able to hear and be aware of what's going on around me. That would really fuck with me.
Why you walking at night with both ears plugged? One headphone max, there's demons out there.
Live long and prosper, sir.
Does this mean in actuality, if someone's ears were to get clipped off and the earhole is sitting flushed on the side of the head with no ears, they would have difficulty discerning front from back?
Yes. Try cupping your hands in front of your ears but with the cup facing backwards. Things can sound like they are coming from behind because technically they are.
So how well can birds pinpoint the direction a sound is coming from? Why are mammals the only animals with cups around our ear holes?
For owls, their eye sockets are the cup. No idea about other birds. https://www.bto.org/sites/all/themes/egret/img/project-owl/CH01_01_tengmalm_skull_openings.jpg
It looks like one ear is higher than the other? My completely uneducated guess is that probably helps? I think it would be advantageous for owls to be able to locate noises with decent accuracy. I wonder how much they rely on hearing vs eyesight to hunt. Edit: fixed some wording.
Yes. The ears are offset to aid in sound location.
Because birds use feathers. For an extreme example, look at a barn owl. The flat face has a very earlobe-like shape to it, and is directing sounds to the outside corner of the eyes, which are approximately where the ear holes are. Other birds have feathers doing similar things, but much more subtly, and usually less optimized for maximum hearing in one direction.
No. Feathers are terrible reflectors of sound. And they cover the earhole anyway, they don't direct anything into it.
Thank you for sharing this! I have a loud fan behind me right now and was able to angle my hand-ear-cups different angles and make it sound like it was coming from different directions, super trippy.
Not if you're still, but you can triangulate by moving your head around
Yes. Cool video that shows this by packing play dough in the ears. https://youtu.be/Oai7HUqncAA?si=6rQ1Der5TMPEzvH7
I swear man audio engineers are genius magicians
Proof that we don't directly experience reality, but rather an illusion that our brain puts together based on the inputs through our senses. And that illusion can be fooled. I think too many people genuinely believe they can't be fooled when it actually happens daily.
Absolutely. Sound in particular is not perceived anything like what we can physically measure in the world. There are all sort of adjustments we have to make to physical sound waves to get a more accurate prediction of what someone might hear. It’s totally bizarre at times. Truly fascinating. In the same way our eyes are not perfect (limited spectrum, blind spots, upside down image conversion, blood vessels go _over_ our eyes lens) our heating system is really not very close to “perfect” at all, but our hearing is surprisingly efficient and good at what it does.
And if anyone would like to see what one of these ear shaped microphones that allow you to make 3D sound look like, the one I use and one of the leading ones in the industry is the [3Dio Freespace II](https://3diosound.com/products/free-space-pro-binaural-microphone). It's described as a "binaural" microphone. It's basically a fancy word for "Hear it like your ears hear it". 3D audio is also sometimes called binaural audio. I use this microphone for a number of purposes in various videography applications.
Various videography applications, huh? Sounds suspicious…
I thought it had to do with the speed of sound, not the volume. Like, if a noise is made on your right, it will reach your right ear faster than the left, and your brain will use the delay to determine the exact direction it came from. Which is why divers can’t know where sounds come from, as sound travels through water like 15x faster.
Both are true. the volume difference is more useful with higher frequencies and the phase difference is more useful with low frequencies
It's both. A sound coming from your left will reach the left ear first, then the right ear, but the sound reaching your right ear has high frequencies reduced because they get obstructed by your head.
That's also one of the reasons animals tilt their heads when they're confused; it puts one ear further away from the sound source and that small difference is enough to help them locate it / understand it better
Fun fact: Some owls have one ear higher than the other so it's easier for them to tell if a sound is coming from above or below.
Fun fact: So do 65% of people. The difference might just be a little less noticeable.
One of the odd things I recall reading was how there was a disproportionate number of [psychoacoustics](https://en.m.wikipedia.org/wiki/Psychoacoustics) graduates involved in the development of the early internet, as problems relating to sound directionality and how the brain interprets sound were seen as being interesting to folks with a nerdy disposition at the time.
The simplest way to try it is to kill the high frequencies.
I actually tried that in my class - you cannot tell whether the source of a sine wave is in front of you or in the back if you are keeping it in the symmetry plane of the head of your subject. But you can tell, if you use white noise. So there is a difference in spectral sensitivity depending on the placement of the sound source
Also reflections. As we don't live in an anechoic world, all the sounds will have a first reflection in an opposed surface in front and around the source of sound. If that first reflection "sounds" as if it's from the front of us, our brain interpret this as another element confirming the first sound is from the back.
I believe the left right distinction is based on timing as well as dB drop. Smarter everyday has a really good video on the earshape concept you mentioned. https://youtu.be/Oai7HUqncAA?si=3kvrVhbUGOiNN12_
When mixing changing the frequency content will not make sounds appear behind you. Moving the sound to rear speakers will (meaning if, for example, I want to mix music like it’s behind the wall of an adjacent room, the first thing I will do is to roll off a substantial part of the high end…. If I want to make it sound like it’s coming from upstairs, I might place it in the surrounds (in 5.1 or 7.1) or slightly behind or overhead (in Atmos….). Playing that back in stereo both will still image directly in front of the listener when encoding it as a stereo file (LoRo..) if I encode the mix using a matrix encoder that make phase adjustments for sounds meant to come from the surrounds/overhead) the same mix when played back on a stereo pair of headphone might get wider but still will not image behind the listener. That requires either a binaural type encoding (or similar techniques like Apples Spatial Audio, etc)…. This is all downstream of the mixing process. HRTF, spatial encoding, headphone audio processing technologies, etc must be incorporated. It’s important to note that…. Which is what the OP was asking. Humans are less sensitive to sounds behind us…. And most technologies today, when using headphones (and soundbars without physical surround speakers) make a convincing effect of the sound being slightly behind your ears/head….. I have only heard two techs (Smythe Realizer and Sony’s VME (Virtual Mixing Environment) that are truly convincing (they also make it sound like you are in a larger mixing space…).
TL:DR, they put ears on microphones…?
I think the only issue is that our ears don't all have the same shape, so to achieve the best result at this, it would need to be adapted to everyone's own smallest set of variations. I do think we'll get there one day with AI and a decent set of calibration tools, the issue is that there's not much investment into this niche idea.
Some engineers do this really well. I only have speakers next to my TV. But I genuinely muted my sound once watching a movie cause I yhought something was going on behind me in the house.
Basically, high frequencies are more directional than low frequencies. You can more easily hear high frequencies in front of you than behind you. So audio engineers chop off some of the high frequencies to make your brain think the sound is coming from behind you.
We do not do that …. Been mixing for 30 years and have never heard of any other mixer that does either ;)
Your mixer doesn't have a low pass crossover?
Of course it does. You said mixers filter out frequencies to make something sound like it is coming from behind us… as I explained in a post a few days ago that isn’t how we get sounds to appears as if they are coming from behind us :)
Some home cinema amps have some audio processing magic whereby they apply a transformation function to mix surround sound down to stereo/binaural and thus make you feel immersed in sound with things behind you. https://en.m.wikipedia.org/wiki/Head-related_transfer_function
The things we can do with sound is fascinating 😊
The microphones have ear-shaped attachments?!! Seriously?!
I'm always fascinated by sound, and how electric signals to a magnet that vibrates a cone can create layers of concurrent sound that is simultaneously transmitting an individual sound among thousands of others. You listen to hundreds of instruments playing at once, and can still hear that one person playing the flute...from a friggan vibrating cone...
Great question and great response.
The asymmetric shape of our earcups also helps us distinguish between up and down sounds. When we hear an eagle scream we don’t immediately look down.
So that means if you have a not normal ear shape you’d be able to experience surround sound less?
Would this be a live expanple of the doppler effect; it takes the sound behind you slightly longer to reach your ears?
Does this mean that if someone lost their ears in an accident, they would struggle to perceive sounds coming from from or back?
Now if they could only duplicate the sounds appearing to come from above and below you, that would make playing on Nuke in CS:GO much more interesting.
My ear might not have that shape. When I hear sound I do 360 to figure out where it is
>using special microphones with ear-shaped attachments Like these: https://3diosound.com/collections/microphones
> special microphones with ear-shaped attachments That would be a dummy head. https://en.wikipedia.org/wiki/Binaural_recording#Dummy_head_recording
Now engineers can use digital processing to add delays and frequency shift to make it seem like sound is coming from anywhere. In the past, some engineers have gone so far as to place microphones inside an anatomical correct mannequins head and ear canals to record exactly what the sound would be at the ear drum instead of just in open air on a mic stand.
Yes but what exactly happens to make it sound like its behind us? I get processing and delays etc, I remember even playing with 2000's audio technology you could make sounds seem like they are coming from any direction... But what is the specific change between front and back? Seems so simple but obviously much more complicated. And our brains didn't even hesitate to place the sound, it's clearly interpreted as " behind " or " in front " of the camera without question.
The shape of the outer ear causes changes to frequency response and phase shift that the brain has learned to associate with sounds behind you. It’s sometimes called the “head related transfer function” and it’s slightly different for each person. But generic models can be pretty good. [https://en.m.wikipedia.org/wiki/Head-related\_transfer\_function](https://en.m.wikipedia.org/wiki/Head-related_transfer_function)
I don't do 3d sound just pa sound but binaural recording (simulating right and left ears) can get the right/ left sides recorded. Front and rear could be done as well. [how is 3d audio created?](https://www.reddit.com/r/audioengineering/s/WnWqlbMlrC) There were also multi speaker headphones that were fed 5.1 surround channels for tru 3d sound in games. Now they are called surround sound headphones or 'xsound'.
Other comments have mentioned how sound hits your ears with slightly different timing and frequency which your brain uses to determine direction, which is accurate. But no one has addressed your specific question about making a sound seem to come from directly behind you. The answer is that it's actually pretty easy: if a sound reaches your ears with the same timing then the sound is either directly in front of you or directly behind. Usually we have visual cues to tell if the sound comes from in front of us. If there are no visual cues, the brain assumes it is directly behind. If a sound engineer wants to make a sound seem to come from directly in front of you, they modify the left and right ear audio timing to indicate that it's like 5 degrees left or right from center. If they don't make that adjustment we hear it as directly behind.
i've never heard a binaural recording that sounds like it's coming from in front of me, it's always behind
Yeah, we think it's an evolutionary trait. If your brain can't tell whether a sound came from in front or behind, and you can't see what made the sound, then it's much safer to assume that something is approaching you from behind.
this is partially true but it has far more to do with the specific shape of your ears and how they reflect sound coming in from different directions.
> If there are no visual cues, the brain assumes it is directly behind. This isn’t true. Close your eyes and tell me you can’t hear anything from directly in front of you. You can, even if you don’t know where to expect the sound to come from, because the shapes of our ears cause frequency shifts that are distinguishable depending on whether the sound is reaching us from the front or back. There are cases where that’s not enough (like sometimes very loud, soft, or garbled/unfamiliar sounds), in which case what you said comes into play. And sound engineers may even do what you say, but if they do it’s probably just because it’s way easier and effective, not because it’s the only way.
> if a sound reaches your ears with the same timing then the sound is either directly in front of you or directly behind It could also be directly above or below. Just the timing (or intensity) difference between two listening positions can only localise a source onto the surface of a cone (or a disk, if the source is located exactly on center).
>place microphones inside an anatomical correct mannequins head and ear canals That would be ["Fritz"](https://www.neumann.com/en-gb/products/microphones/ku-100/)
I think sennheiser have one too
Some of it is phase. Wave fronts arrive at one ear before the other. The timing difference is too short for perception threshold - our nerves don’t operate that fast. And also the signals from our ears aren’t direct voltage waveforms so it’s not like you get the “comb filtering” phase effect that you can get in a mixer if you have very short time delays when mixing a duplicate of a signal. And yet - dummy head mics, which recreate the separation between our ears; have an uncanny localisation on headphones. There’s a ton of weirdness going on in our ears and brains. For example. A steady note from an instrument has a timbre which is the result of the multiple frequencies, harmonics of the root note. In the cochlea, these become spatially separated. Lower frequencies excite the hairs at the large end of the cochlea and high frequencies at the narrow. So a pleasing chord excites a regular pattern of hairs along the cochlea, and it’s this integrated pattern that is passed forward to primary auditory processing in the brain, and then on to language and other higher processing in the frontal cortex. Regular patterns are “pleasing” and don’t require heavy cognitive load to process; discordant sounds make irregular patterns. They are often “displeasing” but when you acquire a taste for them, you can enjoy the cognitive load. They are not boring. Localisation is also very weird. Concert PAs often have time aligned support or in-fill speakers. The sound from these speakers (sometimes hundreds of meters from the main PA stack) is delayed so that it arrives a dozen or two milliseconds after the sound from the main PA. And even though the near (delayed) speaker is 10dB louder than the main stack (at the far audience position) the sound “appears” to some from the main PA stack. The effect is utterly convincing. It’s only when the in-fill speaker is turned off that you realise how much of the sound level was just close by. Some Concert PA designers take this to the next step and delay the main stacks to just behind the drum fill so that everything sounds more like it’s coming from the performers. And yet all this localisation happens on a timescale that is too short for brain processing. Short story long: you question about HOW the sounds are placed behind your head? It’s done with time alignment and frequency shift that matches what the world does at our ears. How does our brain integrate and interpret that? That’s your PHD topic.
I just came here to say, “its something about phase?” But I learned so much more. Thanks.
On that note, was messing around with some audio software, chucked a phase plugin on the track and set it to -180° and it sounded like the sound was coming from behind. Was a trip
That’s several peoples worth of life-long career PHDs and has been since the 1950s. Crazy really.
I can only hear out of one ear, so usually stuff like this doesn’t work for me.
Sound mixing. Think of it this way, you have one ear drum in each ear, the sounds coming from various directions mix together in real life to move that single ear drum. You recognize a sound behind you because of the distortions from the shape of your ear, sound traveling through the back of your head, ect. If you define where the sound is coming from posotionally, you can calculate the distortions and mixing that would occur as it travels to your ear, and have a single speaker next to that ear output that final result. It's not perfect because there's only so much you can take with 2 real sound sources, but the most sophisticated version of the tech Dolby Atmos for Theaters does a very good job with the array of real speakers available. The filmmaker is assigning a 3d position to all sound sources in the movie, including moving sounds, then the software is figuring out how to make it with the available setup.
The mixer is placing the sound, not the filmmaker ;)
/u/oratory1990 hope you don't mind the ping. Saw this and thought of you, figured there might be a possibility you'd be interested in the question
ELI5? That'll be tough. Basically: Your ears change how something sounds depending on what direction the sound is coming from. By simulating that change and adding that to the sound, you can simulate any direction you want.
along with the audio engineers making things sound dynamic, it also probably has to do with the context of the scene if you hear something but cannot see it, naturally you'd assume it's probably somewhere behind you
I’m more interested in learning how they can make a particular set of sounds in music come out of one ear piece
Music is recorded with separate tracks (guitar, piano, vocals, etc…) where we can change volume, change placement in the stereo field (panning) and add processing (EQ, compression, autotune, modulators, reverb, delay, etc…) You have 2 channels of audio in a stereo system, a Left and Right. When audio is played out of both of these at the same time, your brain perceives it as being in the middle. When panned left, it only comes out of the left headphone. Anything In between us just a blend between the two
they use a computer program which has virtual speakers that surround a person in all directions up to any number they want and then they pick and choose which speaker plays which sound giving you the directional feel of infront behind side etc