How spatial audio brings 3D sound to headphones

When Stephen King recorded the audiobook for his classic novella The Mist, he was playing with the predecessor to a technology that can revolutionise audio perception and reduce listening fatigue for headphone users. Welcome to the world of spatial audio…

At Sensors Converge 2024, ipXchange chatted with Seth from CEVA about the remarkable world of spatial audio. This software-based technology enables standard stereo headphones to provide an experience much closer to how we really hear the world around us, but what does this really mean?

What is spatial audio?

As Seth explains, when a typical pair of headphones is panned to the centre – i.e. there is equal signal coming from the left and right sides – your brain interprets the sound as coming from inside your head. But this is obviously not where you usually hear sounds coming from…

CEVA’s spatial audio algorithms bring sounds outside of your head – at least in terms of how you perceive them – without altering the convenience of the headphone experience. You can still use a two-speaker hardware setup!

In many ways, the aim of spatial audio is to make listeners ‘forget’ that they are wearing headphones. In applications such as gaming, this enables the perception of characters in front of and behind the player, providing a far more immersive experience that cannot be done with traditional stereo audio mixing.

Spatial audio is enabled by two main processes:

Spatial rendering – This takes multi-channel audio and uses algorithms to convert it into a representation in 3D space for the stereo mixdown. These algorithms were developed after years of perfecting the subtle changes in audio as heard by human ears on two sides of a head.

Head tracking – This uses an IMU (Inertial Measurement Unit), for example, to track the motion of a listener’s head so that the position of a sound source remains constant relative to the user in 3D space. This is the key to a truly immersive audio experience.

Creating excellent spatial audio perception with just two speakers is not an easy process as everyone’s head is different. The reflections and absorptions of sound sources by a user’s body – reflecting off of their shoulders for example – is also key to creating a realistic experience. While this is still a huge challenge, CEVA is making big waves in this endeavour.

Spatial audio is not simply for the purpose of entertainment.

Non-spatial audio is inherently taxing on the human brain. This leads to listening fatigue as a user’s brain attempts to reconcile where their eyes see a sound coming from and hearing it within their head.

Thanks to spatial audio technology, professional gamers working in headphones for 8 hours a day, for example, are not fighting a disconnect between what they see and here. This mental energy can therefore be used for winning!

How to test CEVA’s spatial audio technology

The headphones you see in the demo are fully equipped to start rendering spatial audio, with built-in motion tracking and Bluetooth connectivity so that you don’t get tangled in cabling. That said, this is only 2-channel audio.

Seth also recommends spatial audio rendering on the host device for a much more immersive experience. The trade-off, however, is latency between the motion tracking and audio, as the spatial render is not done on the headphones themselves and the IMU sensor data needs to ping back to the host.

CEVA’s software can run on hardware as limited as a low-power MCU, and CEVA can help you select the right motion tracking sensor for the most streamlined development using its technology with your choice of silicon.

We truly hope you enjoyed this discussion, and you can learn more about CEVA’s spatial audio and head tracking solution on the official website.

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