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Sound engineer here. If loudness level is the same for both sounds, main thing you will recognize is the timbre. Closest sound will have much more highs than further one, because highs are more easily absorbed by air and humidity itself. Further sounds tend to have rolled off top end.
Also microdynamics are kept with closer sounds, let’s say you have two voices – closest one will have breath sounds, some pops and crackles, you can hear saliva being swallowed and other tiny things that usually slip unnoticed. Furthest voice won’t have any of that.
Another aspect is room reverberation – closer you get, bigger the ratio between reverb and direct sound. Voice far away will sound as loud as room reverb. If you come closer to source, direct signal will get louder and room will stay the same.
Sorry for bad english, its not my first language.
Edit: our mind is one powerful signal processor. We acquire our knowledge and how its sounds even before birth, so a lot of things for our mind are easy, because we are so used to them, that’s why its so hard to understand why we can distinct different sounds. But with good training we are capable even more.
Remembering back to high school physics, low frequency wavelengths will travel further than high frequency wavelengths. When we hear a “sound” it is a combination of many different wavelengths of vibrating air. A sound played quieter and closer to the listener should sound brighter (more high wavelengths retained) compared to the same sound reproduced at a higher amplitude further away.
The shape of the outside part of the ear, the pinna, also helps us differentiate between sounds in front of us and sounds behind us by a similar mechanism. Some audio and electronics companies (eg. Creative, Bose, Samsung and I’m sure many others) exploit this to simulate surround sound from a stereo speaker set up. Like our vision, we have two sensors that let our brain perceive stimulus in three dimensions
I’m a neuroscientist that studies hearing. The main difference would be the difference in intensity (loudness) between your two ears, the Interaural Intensity Difference.
- A sound off to your left but very close will be much, much louder in your left ear than your right ear
A sound off to your left but very far away will be equally loud in both ears.
Your brain has special circuitry in the brainstem that does this math automatically, comparing the differences in intensity and arrival time between the two ears.
The shape of the pinna have nothing to do with localizing distance. Pinna are for differentiating between something in front vs. behind you, and the elevation off of the horizontal plane.
Natural sounds are mainly complex waveforms comprised of fundamental frequencies and their respective harmonics, as well as any additional timbre and tone based additives (yummy). Compile this with the environment they are in and you get additional things that add to the wave known as time based effects. Our ears perceive sonic distances based on time based and dynamic based elements.
Time Based :
The sound reflects off of multiple surfaces getting delayed, confused, and in the end arriving at the ears at slightly different pitches or delayed resulting in various levels of mangle or not-so mangled. Ambiance (and lack of) plays a part when the environment adds reverberation and echos from faint to large amounts. Group all these factors together and in the end our brains can tell calculate which sounds arrived at which ear first, last, or if they arrived at the same time as well as their ambiance structure and place them in our perceived stereo field.
Dynamic Based :
Lower frequencies travel further than higher frequencies. Thats why a voice up close to you quietly sounds crisp, and a voice yelled from across a hall sounds slightly dull (depending on the reflective surfaces). Also, back to the original waveform, a complex wave form will embody whichever character it is being delivered from at its velocity. You can consider the ADSR for Dynamics ( Attack, Decay, Sustain, and Release ), as well as Volume, Velocity, Tone and Timbre.
All these things help us perceive distance, location, and quality of sound.
In addition to the mentioned volume differences between ears, an important factor is that sound waves bounce, causing what is known in the sound engineering world as “reverb”, a certain “muddy”, or unclear, quality of the sound. It happens because unless you are in a completely open or completely padded environment, you hear not only the original source of a sound, but also all its early reflections overlapping in quick succession.
When the source of a sound is nearby, the original wave is much louder than its reflections, because it has travelled (proportionally) much less distance before reaching your ears. Therefore, you hear the original sound clearly.
On the other hand, a distant sound will require about as much distance to reach you as its early reflections, so you will hear several copies of the sound at similar volumes in quick succession, causing the sound to become muddier. Since you are accustomed to muddy sounds coming from distant sources, you will interpret the sound as distant, even with your eyes closed.
Audio engineer here.
Distance is perceived by changes in the timbre of a sound. Boiled down, timbre is essentially the complex, high frequencies that distinguish sounds and make them unique.
Here’s an analogy:
It’s easily compared to looking at a piece of art. Say, if you’re looking at a painting that’s arms length away, you’ll be able to potentially look at each brush stroke or irregularity in the surface of the painting with immense detail. However, if you look at an enlarged version of that painting 50 yards away, you would still see it, but you would undoubtedly have a lot of trouble seeing those same intricate, subtle details as you did when it was at arms length.
Imagine a violin player playing a note quietly immediately in front of you. You would be able to pick up on very discrete, high frequency information that makes up the timbre of that sound. Perhaps you might be able to hear the crispness of the hairs gliding over the bow.
Now if you heard that same sound at the same volume from far away, you might not be able to hear that same level of detail.
Sound waves lose intensity as 1/r^2, similar to gravity. This is basically because your “energy” is traveling as the surface area of an expanding sphere away from a source. This is common in gravity, e&m, etc.
Lets assume that the sound is either directly to your right. A close and quiet sound, like a single headphone, will decay MUCH more significantly. The difference in L-R volume between your ears is greater.
In a far away sound, where most of the energy is already lost (presenting a lower volume to you), there is less loss in the 10 inches between your ears compared to the possible miles the sound has traveled before hand.
Basically, if two sounds have the same apparent volume in your right ear, nearer sounds will be fainter in your left ear and farther, more intense sounds will be more equal across your ears.
Basically its the equivalent of “tidal forces” for acoustics, to bring back the gravity analogy. In this case, its the “tidal volume-difference”.
Many of these answers give you a physics based answer but they do not answer how the brain differentiates sounds. In fact, many of these answers are at least partially wrong in their definitions of timbre, which has nothing to do with our ability to process proximity or loudness. Here’s what we know so far:
The brain can differentiate three components of a wave (first is the actual mathematical component, second is what we interpret it as):
The signal’s amplitude (perceived as loudness)
The signal’s frequency (perceived as pitch)
The signal’s complexity (perceived as timbre)
When sound enters the ears, it will always enter one ear more rapidly than the other due to proximity. Once the proper frequencies are stimulated at the cochlea, the signals are sent to the brain stem. In the brain stem, some signals are sent to what are called the olives of the brainstem. There are two kinds of olives important for hearing: the medial (closer to the middle of the brain) and lateral (towards the sides) olives.
To process the sounds, each of these olives are specialized for a purpose. The medial olives are specialized in determining the proximity of the sound, and the lateral olives are specialized to process the loudness of the sound. So in your case, your brain could process the quiet signal or the loud signal’s proximity and loudness by this manner. Note that there is some crossover in functionality in the brain as well, but this is generally what their specialty is considered to be.
Now there is something that is not well known, and that is how the brain can differentiate between sounds that include the same frequencies at different locations and amplitudes. For example, if you are at a party and there is music and talking, with many of the same component frequencies, how does your brain know how to attribute each of these components to the right people? We’re still working on that!
Acoustics student here. As with direction of sound, the brain simply applies what it measured in previous environments. The brain has an idea of what sounds should sound like and assumes that the difference between what’s expected and what’s measured is due to the environment.
For example, if you’re outside and you hear a gunshot, your brain hears it, relates it to all the things you’ve heard like it in the past, notices that it was missing high frequencies and trailed off gradually rather than all at once. It therefore sends you the message that it’s far away.
The brain doesn’t know why it sounds like this, but it knows that when things sound like this, they’re usually far away. As everyone else is saying, there are a whole bunch of different factors which the brain uses in different cases.
If you can reverse engineer the things that make it sound like that, then you can apply it to whatever you like and trick the brain into sending you the “far away” notice.
Sound encodes a lot of positional information. With a lens, for instance, you could pinpoint the location of sound sources just like you could for light sources.
Without a lens you have to rely on differences in t between when the signal arrived combined with differences in amplitude of those two signals.
If you draw the set of all points that would account for the difference in volume between the two received signals, and the set of all points that would account for the difference in time between the two received signals (left ear and right ear if that wasn’t already clear), and then look at their intersection, you end up with a more or less bounded set. This is a big step, and we actually do this calculation (see passive sonar), but it’s not really good enough to get the information we are capable of extracting.
We pay a lot of attention to echoes as well. sounds that are very close to our ears tend to not have much in the way of echoes. (relative to volume), whereas a sound that comes from far away has many echoes with similar volume as the original signal.
I think passive sonar and acoustics account for most of how we range sounds, but other aspects of the signal such as it’s spectrum, influence how far it can travel. The most obvious example of this is with lightning, and it shows in two ways. The closer the lightning strike is to you, the higher pitch its thunder will have, and the longer you listen to thunder the deeper it gets (because the echoes have travelled farther). Assuming you have some information about the sound you are supposed to be receiving, you could also use this method to range it.
It is true that the timbre of the sound would change over distance (due to low frequencies travelling farther) but I think the MAIN difference would be in the reverberation/delays we hear from sounds far away.
I work with live sound and do sound recording as a hobby, and the best way to make something sound “far away” in a mix is through reverb. When sending a signal through a reverb processor, you can adjust how “wet” or “dry” thie signal is. A 100% dry signal would be only the original source, while a 100% wet signal would be only the reverb, none of the original. The more “wet” the signal is, the farther away it is perceived to be, because you are hearing a higher ratio of reverb to original signal. If a sound is very far away, most of the sound you hear has bounced of other objects along the way. You hear very little of the “dry” sound. So your brain decides that a sound that is mostly reverberated is far away.
Think about listening to a person talking in a room. If they are standing right next to you, you hear the “dry” signal from their voice, and it drowns out most of the reverb you would hear. If they are at the other end of the room, a larger percentage of what you hear is reflected off the walls and ceiling rather than coming straight from their mouth.
It all has to do with how fast the sound waves hit each ear and how loud it is. Using this our ears can localize where the sound is coming from. If something is directly in front of you, it’s hitting both ears at basically the same time. If something is to your left, it hits your left ear first, the sound does go sort of through your head to your right ear, but most of it goes around your head. Your ear hears it even more when the sound gets around your head and also when the sound bounces back off of say a wall and back to your right ear.
At super low frequencies, we have very little ability to distinguish where noises are coming from.
About 20 years ago I wrote a science fair paper about how all that was needed to electronically reproduce surround sound was two speakers. All because of the way that our ears are shaped. The shape of the ear is so that we can tell weather sounds are in front or behind, and combined with stereo hearing from two ears, we are able to localize any sound in three dimensional space (perhaps with some head movement for verification.). NONE of the judges believed it was possible to determine the direction a train was traveling from directly underneath! I got third place. But looking back I realize I had zero sources for any if my claims…