In 8D audio, how is the audio able to sound like it’s behind or in front of you even though there are only left or right outputs?
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Hearing scientist here. This one gets asked in various formats quite a bit (I’ve answered it a few times).
Basically, everything we hear is a stereo (LR) signal by the time it gets to our ears. But our ears (and brain) are very good at decoding this to work out position.
In terms of surround sound, etc., the aim is to create a soundscape in the room that is as similar as possible to the real world, from the perspective of the relevant listening position(s). That is, if you’re sitting in just the right spot, the waves arriving at your ears is as close as possible to if that bird was actually real, or if that car really drove past you, etc. This is done using complicated maths that makes the sound waves from different speakers interfere with each other, adding up of cancelling out in just the right ways.
As for how your ears work out where thing are (real or virtual), there are a few different ways:
1. We can detect tiny differences in arrival time between the ears. A sound on your left reaches your left ear before your right ear. This is called the Interaural Time Difference (ITD).
2. We can detect tiny differences in volume between the ears. A sound on your left is louder in your left ear than in your right ear (partly due to your head casting a shadow). This is called the Interaural Level Difference (ILD).
Both of these help discriminate left and right, but not front/back or up/down. If a sound is anywhere on the flat plane between your ears, it’ll sound the same to each ear. So directly in front will arrive simultaneously at L and R, as will directly behind. So, we also use:
3) Motion cues. By moving your head around (which you’re constantly doing, even if you’re trying not to), you break the symmetry. Turning left will mean a sound in front of you is now to your right, but a sound behind is to your left. Tilting to one side or the other breaks the up/down symmetry in a similar way. We use balance organs in the ears to work out how we’re moving, and interpret the apparent motions of sounds.
4) Spectral cues. As other have mentioned, the shapes of your *pinnae* (the flappy bits of your ears) play a role. These act as filters to different frequencies of sounds depending on location. For example, a complex sound will sound slightly tinnier (more high end) in front of you, but more bassey (more low end) behind you.
Each of these has its limitations. ITDs only work for low sounds or complex sounds. ILDs only work for high sounds. Motion cues rely on…motion, but also balance. Spectral cues need to be for complex sounds, preferably higher pitched. But, together, they mean we are ridiculously good at pinpointing sounds in front of us. Off at the side, we’re not so great, but we can at least turn to face the source. After all, of a lion is somewhere on your left, you probably don’t care too much about a 5° difference!
Edit: Thanks, kind strangers 🙂
Edit2: Rule 4 – Don’t literally explain to a 5 year old! But [here](https://www.reddit.com/r/explainlikeimfive/comments/ldzj17/eli5_in_8d_audio_how_is_the_audio_able_to_sound/gm9sr07?utm_source=share&utm_medium=web2x&context=3)’s an attempt anyway!
I’m not an expert, but broadly, it’s similar to the way that our eyes can combine two flat images into a 3D view of the world.
Ears are able to pick up extremely small discrepancies, including the timing difference of the sound’s arrival at one ear versus the other.
The head itself also acts as a “stereo separator” of sorts. The ear further away from the source of sound will hear a version of the sound that is more faint and tonally different from the other ear, and the brain can synthesize these discrepancies.
Clever recording and mastering technologies can make use of this biology, sometimes by literally recording with microphones placed inside a “head”. Other times, they’re able to use software to adjust the audio and add these directional cues artificially. This is why these technologies only work with headphones. They need complete control over what each ear is hearing.
8D audio is not actually 8D it’s just stereo (L and R)
That moving effect is simple. instead of just panning audio from left to right without stereo leak it takes advantage of it.
Audio moving from left to right without stereo leak
1. ((((L)))) > R
2. L > ((((R))))
Simple but not that great when you want realistic sound
With the effect
1. ((((L)))) > R
2. (((L))) > (R)
3. ((L)) *phantom center* ((R)) audio shared equally on both channels creates phantom center
4. (L) > (((R)))
5. L > ((((R))))
With added reverb and room effects. it makes your brain think its coming from behind and front revolving around your head even tho it’s not..
Hope this helps sorry for the shitty explanation
Ill try to explain it the way I would explain it to myself honestly. It will have to be in stereo not mono, meaning it will play through left and right. 8D is t actually a think it’s just what they called it. And you can manipulate how far away it sounds or where you hear it through something as simple as panning and reverb
Simple explanation, we only have left and right inputs. So if you output the sound in the right way you will hear it the same as if it was actually coming from the direction they intended.
I also have a question related to this…
Why do all 8D songs seem to just move from left to right and back again? It sounds cool, but they all just do the same thing and it gets a bit difficult to enjoy after a while. Does anyone have links to some really good 8D sounds/songs that really show off the technology?
There are many technically detailed answers here but almost none answer the question exactly, probably because they don’t know what 8D audio really is. 8D audio is not an official standard or anything, just a clickbaity term many YouTube channels have adopted. It’s nothing more than slowly panning different instruments from left to right audio channels and vice versa.
But you are right. You can’t actually tell if a sound is in front of you or behind you with just a stereo channel. Even with 8D audio. What happens is you subconciously “decide” whether the initial sound is in front or behind you, and then go from there.
If you focus enough you may be able to change the direction of the music from clockwise to counter clockwise or vice versa (in the same way you can change the direction of that spinning ballerina gif illusion if you think hard enough, if you’ve seen it – it is the same concept, with a 3D animated object being displayed on a 2D plane, but using image instead of audio).
If you are thinking about buying a piece of audio kit and it says its 8D and you actually believe there are 8 dimensions well, I guess you deserve the audio quality you are about to get.
The shape of your ears causes sound to distort when it comes from different angles.
The speakers emulate such a distortion and thus can make it sound like its coming from behind you, despite only having speakers directly in front.
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