How does surround sound work on headphones?

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I understand how Dolby Atmos works on 5.1 and 7.1 systems, but wouldn’t translating it to headphones just make it standard stereo? Headphones only have two speakers, one on the left and one on the right.

Even without head tracking like Apple’s spatial audio, why does surround still sound different from stereo?

In: Technology

No matter how many speakers you’re working with, you only have two eardrums. Your actual sense of hearing is stereo, and the “surround-ness” is post-processing applied by your brain.

The basic gist is that your brain uses the delay between a sound being heard by one ear or the other to determine left-right placement of the source, and whether or not it’s muffled by the flesh of your ear to determine front-back.

Virtual surround sound processing just modifies the sound in approximately the way your brain expects it to be modified, and then pumps that directly into your ear.

This one gets answer fairly often in various forms. [Here](https://www.reddit.com/r/explainlikeimfive/comments/ldzj17/ELI5%3A_In_8D_audio%2C_how_is_the_audio_able_to_sound_like_it%27s_behind_or_in_front_of_you_even_though_there_are_only_left_or_right_outputs%3F/gm8vmzd/?utm_medium=android_app&utm_source=share&context=3) is an answer I gave before that people seemed to like.

Short version, you’re always only listening to left and right because you only have two ears. The trick is just in how to make the right combination of signals at your ears. Multiple speakers let you physically make sounds come from different directions. But you can also manipulate the sounds themselves to give that effect.

You only have **two ears**. Seems like stereo, right? But you hear the real world in full 3D.

It’s because sounds from different directions will hit your ears at different times and will be filtered differently through your head, and your brain knows how to interpret this and convert it to 3D perception.

So, audio companies can use HRTF (head-related transform functions) to make sounds sound like they’re coming from any direction. This is why HRTF 3D requires a special processor/software, like the Astro A40 MixAmp, because it’s translating the surround signal data into HRTF *instead of* directly sending signals to a bunch of little surround speakers.

You only have 2 ears. 2 sound sources is all you need to hear full real 3D. *If they’re processed* in a certain way.

This is why multi-speaker “surround” headphones are a scam. But people don’t understand ears or sound perception, so they think they need multiple speakers and they have no clue about HRTF.

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