Dr. Henney Oh, co-founder and CEO of spatial audio specialist G’Audio Lab talks us through the processes of capturing, mixing and rendering sound for virtual reality and 360-degree video applications.
The premise of VR and 360-degree video is to simulate an alternate reality. For this to be truly immersive, it needs cogent sound to match the visuals. Humans rely heavily on sound cues to inform us of our environment, which is why immersive graphics need equally immersive 3D audio that replicates the natural listening experience. The challenge becomes how to draw the viewer’s attention to a specific point when there is continuous imagery in every direction, and sound cues can help with that.
The key to creating realistic audio for this is to synchronise sounds according to the user’s head orientation and view in real time. This helps replicate an actual human hearing mechanism, which makes the listening experience more realistic. Producing truly immersive sound requires several steps. First, you must capture the audio signals, then mix the signals and finally render the sound for the listener.
To replicate the natural listening experience, the use of two audio signals – Ambisonics and object – is essential.
Ambisonics is a technique that employs a spherical microphone to capture a sound field in all directions, including above and below the listener. This requires placing a soundfield microphone (also known as an Ambisonics or 360 microphone) somewhere near the position where you intend to listen to. Keep in mind that these microphones will record a full sphere of sound at the position of the microphone, so be strategic with where you place them. It’s also important that your mic is not spotted in the scene, so we encourage placing the microphone directly below the 360 camera.
In addition to capturing audio from a soundfield microphone, content creators also need to acquire sounds from each individual object as a mono source. This enables you to attach higher fidelity sounds to objects as they move through the scene for added control and flexibility. With this object-based audio technique, you can control the sound attributed to each object in the scene and adjust those sounds depending on the user’s view.
Capturing mono sound can also be tricky because the traditional use of a boom microphone to capture mono does not work in VR. In synchronised 360 sound recording, there is no space to place the boom microphone, so it is helpful to place a lavalier microphone directly on the individual (hidden underneath apparel).