What is 3D surround sound virtualization?
[ Info Guide ]

Playing games and watching movies on headphones often involves using various software surround sound virtualization algorithms present on most sound cards or in the games itself - like for example Creative's SBX Pro Studio Surround, CMSS-3D, Asus' Dolby Headphone or other built-in technologies like Dolby Atmos for Headphones, Windows Sonic for Headphones.

If you first heard of some of these names, you are probably very confused what they actually are and how they work. It's not actually magic, like they are telling you in all those colorful expensive ads. These kind of algorithms actually exist since some time ago and are very widely used in the audio industry. Even the game's audio engines themselves utilize them - so technically if a particular game's audio engine has a good surround sound virtualization algorithm, using also an external one from your sound card's software on top of it could potentially sound worser than actually advertised (in that particular game).

That's why it is so important to test them in every single game and compare which one actually sounds better for you.

Most of the surround sound virtualization algorithms - especially for headphones - utilize all the mathematical, physical and psychoacoustic knowledge gathered about HRTF (Head-Related Transfer Function). From wikipedia:

Humans have just two ears, but can locate sounds in three dimensions – in range (distance), in direction above and below, in front and to the rear, as well as to either side. This is possible because the brain, inner ear and the external ears (pinna) work together to make inferences about location. This ability to localize sound sources may have developed in humans and ancestors as an evolutionary necessity, since the eyes can only see a fraction of the world around a viewer, and vision is hampered in darkness, while the ability to localize a sound source works in all directions, to varying accuracy, regardless of the surrounding light.

For more details, you should check the whole article on HRTF on wikipedia. But very shortly and more generally it means, that it's fully possible to hear a 3D surround sound environment just like in real life by using just your headphones - assuming the right algorithms to virtualize this environment are used. More specifically - the right algorithms suitable for your individual ears, because every person hears differently.

So if it's fully possible, then why most of the games, music and movies don't give such amazing and natural 3D sound immersion on headphones? That's actually a very valid question. And the reason is very simple, straightforward and also a bit sad: Most of today's media (music, movies, games, TV programs) are designed [recorded, engineered, mastered] from the beginning to be listened to on multi-channel [movies, games] or stereo [music, TV programs] speakers. Headphones are different in the way they work than speakers - most notably and most importantly, only one speaker can be heard by one ear at once - and they are also stereo. Even the marketed "5.1" or "7.1" headphones are actually in the end only stereo, despite having multiple drivers.

So if you would want to have a good-sounding natural 3D effect in games, movies and music on your headphones the whole source would have to be also separately engineered for headphones to sound correctly on them. But this way this separate mix wouldn't sound correctly and naturally on speakers. So in the end, as a compromise, as always won something which is just more popular and optimal - and that means the speakers won.

Separate mixes and recordings only for headphones of course also exist, but they are not so popular - they are called binaural recordings. They are made using a special dummy-head, which simulates how our ears and brain percieves sound from the environment. These recordings are made only in stereo - because humans have only two ears, and really no more tracks and drivers than two are needed to percieve a natural surround sound 3D effect on headphones (if they are made properly). Here is such an example of a binaural recording.

Using native binaural recordings or appriopriate 3D surround virtualization techniques for headphones is extremely rare in games, and almost non-existent in movies. The closest to real binaural recordings you will usually hear in games and movies will be for example ambient sound recordings.

One of the (often neglected) problems of surround sound virtualization algorithms and binaural recordings is that there are many different physical models for it, and not every implementation will work good for all listeners. So if you think that some of these techniques or sample files don't sound too good or natural for you - don't worry, it's completely normal.

Because of such dependence of 3D sound virtualization on headphones on the individual listener it's likely to assume that the more generic approach to creating surround sound in games and movies (on speakers) will still remain more popular. Unless someone will find a way how to quickly personalize the sound on the fly to our own individual hearing, the current non-ideal techniques will just have to remain with us.

Today there are several attempts to popularize 3D surround sound virtualization techniques.
For example in Windows 10 Version 1703 Creators Update Microsoft added platform-level support for spatial sound processing including Windows Sonic for Headphones and Dolby Atmos for Headphones. The last one works by converting all Atmos channels into a virtual Binaural 360° output using the usual two headphone drivers. This technique is an improvement on the previous Dolby Headphone technology, though mainly because it simply adds the extra Atmos channels. And it's also not a free technique - before using it, you have to buy a license.

Keep in mind however, that even multi-channel (5.1 or 7.1) speakers are still very weak in reproducing sound from above and from below - because they are meant to be set in just one totally flat horizontal line. Therefore one very significant advantage in binaural recordings and 3D surround sound virtualization techniques for headphones is that for them both above and below are never a problem - they just work out of the box.

This and also that headphones are much cheaper and easier to setup properly in a typical room than a big home cinema speaker setup, is why these virtualization techniques are becoming progressively more adopted into competitive multiplayer games.
(for example Overwatch includes built-in Dolby Atmos for Headphones in the audio options)

Thank you for reading

If you liked this topic, you might be also interested in this guide:
How to properly configure 3D surround sound virtualization for headphones in Windows Vista/7/8/10. [ Guide ]

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