Ambisonics

What is it?

Ambisonics is a speaker-agnostic spatial audio format. Instead of recording separate tracks for specific speaker positions (like 5.1 or 7.1 surround), Ambisonics encodes the complete 3D sound field as a set of mathematical components called spherical harmonics. These can then be decoded to any speaker layout — a dome with 24 speakers, headphones, a stereo pair, or a VR headset.

It was originally developed by Michael Gerzon and Peter Fellgett in the UK in the 1970s, but has had a major renaissance with the rise of VR, 360° video, and immersive venues like planetarium domes.

Orders of Ambisonics

The "order" determines spatial resolution — higher order = more precise directional accuracy.

Order	Channels	Use case
1st order (FOA)	4 ch	Basic VR, 360° video, entry-level domes
2nd order	9 ch	Improved localisation, mid-tier domes
3rd order (HOA)	16 ch	Professional dome standard — Jena, SAT, most festivals
5th order	36 ch	Research / high-end installations

Most fulldome festivals specify 3rd order HOA (16 channels) as their audio delivery format.

Channel Conventions: ACN / SN3D

Two "dialects" exist for how channels are ordered and normalised:

• ACN/SN3D — the modern standard (used by Google, YouTube 360°, most DAW plugins including IEM suite, dearVR, Reaper AmbiX). This is what festivals expect.
• FuMa — the legacy format from the 1970s originals. Still found in older tools (some older Max/MSP patches, SoundField mics). Needs conversion before delivery.

When in doubt: AmbiX = ACN/SN3D. Deliver AmbiX.

B-Format vs. A-Format

A-format is the raw microphone capsule output from an Ambisonics mic (e.g. Sennheiser Ambeo, Zoom H3-VR). You never deliver A-format — it needs to be encoded to B-format (the Ambisonics math representation) first, using the mic manufacturer's encoder plugin.

B-format is what you work with in your DAW and what you deliver to festivals.

Playback: Decoding

The genius of Ambisonics is that the encoded file doesn't care about the speaker layout. At playback time, the venue applies a decoder that maps the sound field to their specific speaker positions. This means your mix sounds right whether the dome has 8 or 80 speakers — as long as they have a proper decoder.

Common decoders: SPAT Revolution, IEM AllRADecoder, IRCAM Spat, venue-proprietary systems.

Ambisonics in the Dome Workflow

1. Create or record audio sources (MIDI synths, foley, location recordings)
2. Position each source in 3D space using a spatialiser plugin (e.g. IEM Suite, dearVR, 360pan Suite)
3. Sum everything into a 3rd order Ambisonics bus (16 channels)
4. Export as multichannel WAV — 16 channels, 48kHz, 24-bit minimum
5. Deliver alongside your video file

Binaural Preview

To check your Ambisonics mix on headphones during production, apply a binaural decoder on the master bus. This renders the full 3D field to stereo headphone audio using HRTF processing. Remove the decoder before final export. See also: Binaural Headphones →

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