Binaural Audio- Understanding Its Importance, Precision & Virtual Applications

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Binaural audio is a term you have probably heard thrown around here, there and everywhere. You may have listened to a sound file or piece of music labelled as ‘binaural’ and felt disoriented by just how real and up close it feels to your ears, even though you’re only wearing the same set of headphones as you usually do.

But what exactly is it?

Binaural audio is stereo audio that’s recorded like we hear it. It’s audio with just the right frequencies and panning to trick our minds into thinking we’re hearing something coming from outside of our headphones. It’s “virtual reality for your ears” as some may call it; just as a VR headset can trick your eyes into thinking you’re somewhere else, this amazing audio tricks your ears and your mind. Check out this video to really hear the magic in action (note: for best experience, watch with headphones).

History

IN PROGRESS

How are binaural recordings made

Most typical stereo recordings are captured with the microphones at arbitrary angles and distances apart. Binaural audio, on the other hand, requires a specific recording setup for it to be exactly that, and not just bog-standard stereo.

The dummy head technique is perhaps the most common method for creating a truly binaural sound. Inside a model of an average-sized adult human head sits two small microphones, specifically where the inner part of the ears would be. This head is insulated to make the captured audio signal really sound like it’s entering the inside of your head from somewhere other than your headphone buds (you’ll understand how and why later).

Nowadays, there are individual microphones on the market that are capable of recording audio with binaural quality without the need for a dummy head. These microphones consist of two capsules positioned at a distance of the average human’s ears from each other with appropriate insulation (and shaped like ears to boot). Many ambisonic microphones also support binaural format, with internal equalisers manipulating the audio in a way.

Why does it sound so real?

As you may have heard, binaural recordings don’t sound like typical stereo recordings. It’s not just how the sounds are panned in the stereo field; there’s something about the captured audio signal itself that sounds more alive and uncanny. But what is that je ne sais quoi? Simple: Head-related transfer functions (HRTF). Don’t worry, it’s actually simpler than it sounds!

When something makes a noise, it emits multiple sound waves that travel in all different directions. When one of us is there to hear it, some of the sound waves may enter the ear directly, while others bounce off from elsewhere and hit us from a different angle.

Once the sound waves do arrive to us, their frequencies are transformed by the head, ear, ear canal and sinus cavities. Some are boosted and some are attenuated, and it’s this effect that makes sound really feel like it’s up close to us.

How can we use binaural audio?

ASMR

ASMR stands for autonomous sensory meridian response, and it’s described by those who experience it as a pleasant tingling sensation on the skin that starts at the scalp and runs down the spine. It is usually triggered by hearing particular sounds such as soft whispering, tapping fingernails on a surface or crumpling up paper.

YouTube videos created specifically to trigger ASMR have permeated the Internet and amassed a global following of millions. Many content creators within the ASMR community record the soundtracks of their videos using binaural or ambisonic microphones, not only to intensify the crispness and natural ‘colour’ of the sound effects, but also to offer their audiences a more intimate experience (i.e. as if the creator is actually whispering into the viewer’s ear).

Virtual reality applications

You might be wondering: why would you need binaural audio at all for a virtual reality environment when surround sound exists?

Well, there are times when a developer may want to position a virtual object right next to the listener, or craft an interactive object entirely from sound! Binaural audio allows you to do just that, and place directional audio on an object as if it’s right up against your ear or at your feet – this is something  surround sound simply can’t do.

This 3D stereo setup is by no means a replacement for surround sound, however. Because binaural audio is optimised for speakers close to the ears such as headphones or earbuds, the illusion of presence may be lost if projected over even the most impressive surround sound speaker setup. Therefore, for ambience and other sounds enveloping a large amount of space, surround sound just has the edge.

Therefore, both forms of audio are fantastic, and should be used where possible within your immersive application together, since both have their advantages and disadvantages. With surround sound for ambience and binaural recording for close-up sounds, our brain processes these two different audio types together, creating a more captivating soundscape and realistic sense of presence.

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