Welcome to ‘Kagoo Explains’ - a series of short articles de-mystifying some of the confusing terminology used to describe tech. This week we’re looking at virtual surround sound, and explaining how your soundbar can trick your ears into thinking you’re inside a movie!
When you’re buying a big screen TV to immerse yourself in the latest movies, it’s worth taking the time to make sure the audio is as powerful and capable as the visuals! Surround sound can make you feel like you are inside the TV, with audio appearing from the sides, above and even behind you! Traditionally, gaining this ‘3D’ aural experience for your movies and television was costly and fiddly - however the current generation of soundbars is capable of ‘virtual’ surround sound, allowing them to generate a 3D effect with ease! Let’s dive in and find out how:
‘True’ Surround Sound vs Virtual Surround Sound
First, a clarification. The traditional way of setting up a surround sound system involves several individual speakers, all placed around the room and angled towards the listener, so as to ‘surround’ them. This means the audio from the TV can be played from all angles: e.g - when a sound effect needs to come from the right-hand side, it is physically played through the right speaker.
As you might expect, this can get very expensive - since you will need up to 7 additional speaker units - and can be a right faff to set up. It requires quite a lot of space in your room - speakers have to be set at correct heights and angled very precisely, and some systems even require you to mount speakers to the ceiling!
All of this effort is worth it if you’re aiming to set up a professional-level home theatre system, but it’s not for everyone. The barrier for entry on expenditure, time and effort is just too high - so companies looked for a cheaper, easier alternative. Enter the ‘virtual’ surround sound system - which aims to create a similar effect with only 1 or 2 speakers, all powered by a single soundbar and a lot of aural wizardry!
You may have seen ‘5.1’ or ‘7.1’ mentioned when talking about surround sound systems. These refer to the most common physical speaker setups: 5.1 surround sound uses 5 speakers (front, front-left, front-right, rear-left & rear-right), while 7.1 surround uses 7 (adding a centre-left and centre-right to the mix).
The .1 refers to an extra channel used exclusively for ‘low frequency effects’ - these are the super-low bass rumbles. Depending on the setup, this may come from the main front speaker, or a separate subwoofer.
Sound is complicated, and our perception of sound even more so. While the act of a sound wave reaching your ear is entirely mechanical, things get a bit more complicated once your ears and brain come into play, since it becomes a sensory event that can vary from person to person. I’ve summarised the basics below - if you want to read more, HowStuffWorks has an excellent article on How We Perceive Sound.
The act of perceiving a sound involves the sound waves hitting your ear, and creating waves of vibrations that travel through the ear canal until they hit the cochlear nerve. Once there, the waves are converted into neural stimuli and sent to the brain for processing.
If you’re interested, the action of a specific sound wave hitting the ear has the rather charming technical name of ‘Head-Related Transfer Function’, or HRTF.
This processing involves a multitude of different criteria, including ascertaining the loudness of the wave, whether it contains words in a known language, if it is musical with a recognisable tune, etc. What interests us though, is that at the same time the brain tries to work out exactly where the sound came from, a process known as ‘Sound Localisation’.
When analysing a sound, the brain considers a variety of different factors, including differences in loudness and delay between the two ears - these are known as ‘Aural Cues’. The brain is capable of sensing minute changes in the stimuli it receives, and compares the discrepancies to gain a better understanding of the source of the sound.
To give an example - if there is a knock on a door to the right of you, the waves of sound from that knock will travel through the air and hit your right ear before they hit your left. Moreover, the power of the sound will have weakened fractionally by the time it hits your left ear compared to the right, so it will be quieter. Your brain analyses the differences between the stimuli coming from the left and right ears, and decides the knock has come from the right. The differences in volume and delay between the ears are known as the ‘Interaural Level Difference’ and the ‘Interaural Time Difference’.
The entire field of how the brain perceives sound is called ‘Psychoacoustics’, a name coined by the German psychologist Gustav Fechner in 1860. If you want to read more, here is a fascinating overview of the history of the field written for ‘Acoustics Today’.
All of this happens subconsciously, and almost instantaneously - you rarely consciously think about the source of a sound, you just know it’s coming from the right or the left. It is this system of comparison between left and right ears that allows audio engineers to ‘trick’ your ears into thinking a single soundbar is producing sounds from all around you.
Tricking Your Ears
So back to soundbars:how exactly do people like Samsung and Bose make a single set of speakers in front of you sound like 5 or more speakers all around you? In short, they make use of the aural cues the brain is looking for, and carefully tailor the sound from the speakers to send very precise aural cues to provoke a sound localisation reaction from the brain of the listener.
The method of doing this depends on the precise kind of soundbar, and how many channels (effectively a group of speakers) they have to work with. Therefore some smaller 2-channel speakers add an imperceptible delay and change of volume to either the left or right channel, in order to trick your brain into thinking it is hearing a sound from a direction, even though the source is directly in front of you.
However the best ‘virtual surround sound’ soundbars work by angling the individual speakers on the bar in different directions, and physically ‘bouncing’ the sound off the walls of your room and into your ear. Because the sound appears to be coming from a specific angle, the brain perceives this as a directional sound, and the surround sound effect is created!
While these normally limit themselves to the horizontal plane, a tech called ‘Dolby Atmos’ uses upward-firing speakers to bounce waves off the ceiling, in order to create the illusion of sound above you. This helps create a ‘3D Sound’ effect, and is used increasingly for films, with sounds like helicopters passing overhead.
The Limits Of The Illusion
While very impressive, virtual surround sound technology is ultimately just a clever illusion to trick the brain into thinking it’s hearing something that isn’t there. And like all illusions, the virtual surround sound experience quickly falls apart when pushed outside it’s limits.
Because virtual 3D sound requires your head to be at a precise point - usually sitting in front of the soundbar and looking forward - the effect won’t work as effectively if you move your head slightly, or change the angle you’re sitting on the couch. Moreover, soundbars that rely on bouncing waves off walls will have limited effect in very large rooms - or rooms with unusually-shaped walls - since the reflections won’t reach your ears in the intended way.
All of these are definite limitations, but when properly set up, a single soundbar can create a very convincing imitation of a full surround sound setup, with the ability to 'hear' sounds coming from the left or right, or even above or behind you - all from a single source.
Conclusion: A Cost-Effective Imitation of ‘True’ Surround Sound
So in the final analysis, is virtual surround sound as good as a full 7.1 setup? No, it most definitely isn’t. You won’t get the full depth of sound and immersion of ‘true’ surround sound, and the effect is easily shattered by moving your head or body.
However the illusion it creates is powerful, available at a fraction of the cost, and with no need to rip apart your living room to install speakers in the ceiling. It’s a way of anyone gaining the surround sound experience, and for that you can ignore the occasional moments where your brain refuses to believe the magic trick!