Capturing the Entire Soundfield 🌐
Higher-Order Ambisonics (HOA) represents a fundamentally different approach to surround sound. Traditional formats are channel-based (like 5.1, where sounds are sent to specific speakers) or object-based (like Dolby Atmos, where individual sound ‘objects’ are placed in a 3D space). Ambisonics, by contrast, is a scene-based format. It doesn’t record individual channels; it records a mathematical representation of the entire soundfield at a single point.
This is typically done with a special Ambisonic microphone, which has multiple capsules arranged in a sphere. The raw recording is encoded into a format called B-format, which contains all the directional information of the soundfield.
The Power of ‘Higher Orders’
The ‘Order’ in HOA refers to the spatial resolution and accuracy of the soundfield.
- First-Order Ambisonics (FOA) is the simplest form, using 4 channels of information. It creates a sense of space but can be somewhat blurry and imprecise.
- As you move to Higher Orders (2nd, 3rd, 5th, etc.), the number of channels in the B-format file increases (e.g., 9, 16, 36 channels), capturing a progressively more detailed and spatially accurate representation of the soundfield.
The Killer App: VR and Interactive Media
The true power of HOA is revealed during playback. The B-format file is completely independent of any speaker layout. A ‘decoder’ is used to translate the Ambisonic soundfield to whatever system the listener is using—from stereo headphones to a full Dolby Atmos setup.
This makes it the perfect format for Virtual Reality (VR) and 360-degree video. As the user turns their head, the decoder simply rotates the soundfield in real-time to match their orientation. The sound of a bird behind you will stay behind you as you turn to face it. This seamless, head-tracked audio provides a level of immersion and realism that is impossible to achieve with channel-based formats, making HOA the professional standard for interactive audio production.