Ambisonics: An Untapped World Of Full Dome Surround Sound

Ambisonic immersive full dome audio

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When we hear a sound in the real world, we can get an idea of where exactly it’s coming from: in front of or behind us, to the left or the right, above or below us, and right up close or far in the distance. When we listen to a piece of music or watch a TV show with our headphones on, however, we don’t get that full three-dimensional experience. Surround sound systems are getting better and better, but even then they can’t give us that exact same sensation.

This is where the Ambisonics audio system: a true 360-degree sound system where listeners can hear impressive sounds from every thinkable angle, in every thinkable direction (including height!!).They can take your immersive applications one step higher, and introduce your users to a whole new world of sound…

A brief history

The concept of Ambisonics was devised in the 1970s by a group of British academics, including the mathematician Michael Gerzon. Later on in the decade, Gerzon would go on to partner with fellow engineer Peter Craven to develop the world’s first Soundfield microphone.

Though it took a very long time for the technology to catch on (and even today, it’s still more niche than we think it should be), a few immersive content developers have recently begun taking advantage of ambisonics in their applications.

  

How does Ambisonic audio work?

A Soundfield microphone typically consists of four subcardioid capsules positioned in what’s known as a tetrahedral array. This fancy term actually just means the capsules point in different directions, recording sounds both horizontally and vertically from the microphone. The raw recording signal is often referred to as the ‘A-Format’. 

Soundfield microphones also come with a built-in decoder that converts the A-Format recording into a B-Format one; you can think of the decoder as mapping the audio onto some sort of matrix.

B-Format audio is actually made up of four separate signals, one for each axis. Some say it’s a ‘speaker-agnostic’ format, because the decoder can output the signal to a sound format suitable for virtually any speaker setup: mono, stereo, 5.1/7.1 surround sound etc. This makes the Ambisonics recording process an extremely flexible one, where it’s easy to adapt your audio for whatever setup you want to play it out of.

The different axes of the audio recording also mean that the resulting sound can blanket an entire 360-degree space consistently. A typical surround sound setup tends to have more speakers at the front of the listener than anything else, so can sound a bit top-heavy (not to mention the back channels tend to be reserved for special effects). This is not an issue for an Ambisonic recording: you could set your sound up to be projected more uniformly, allowing for an even more engaging listening experience!

What about the disadvantages?

Though Ambisonics is a simple way for you to get your audience lost in an amazing soundscape, it’s ultimately not without its disadvantages that are important to keep in mind.

 It does everything itself

The Soundfield microphones needed to create Ambisonic audio decode the signal by themselves. You may think that sounds like an advantage, as it can save you a lot of time and effort in setting things up…but it also means the decoding process is out of your hands. Because the decoder is programmed to fine-tune audio frequencies and channels in a particular way for each speaker setup, you’re not given as much control over editing the result yourself as you perhaps would be with traditional surround sound setups.

Large file sizes

Because a B format audio recording is much more complex in nature than your standard WAV or MP3 file, you need to allocate more space for it on your harddrive!

Most importantly: we don’t hear enough about it!

When we mentioned earlier that Ambisonics is a niche technology, we really meant it. Outside of academic and specialist circles, it’s almost unheard of, and only now are virtual reality developers beginning to realise its full potential.As developers of their own Soundfield recording microphones, RØDE have developed a fantastic library of Ambisonics learning resources, which we recommend checking out for more information. They’ve even released a sound library with free-to-use Ambisonics audio ready for your own VR portals!

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