Ambisonics Formats at a Glance

johannes.schuett@zhdk.ch (Johannes Schuett) — Fri, 01 May 2026 00:00:00 +0000

Ambisonics uses the word format for several different things at once: the raw microphone signal, the spatial encoding convention, the channel ordering, and the normalisation. This page puts all of them side by side.

All formats A vs B-Format FuMa vs ambiX Orders & channels Normalisation ICST recommendation

All Formats at a Glance

Format	What it is	Channels	When you encounter it
A-Format raw	Raw capsule signals from a tetrahedral microphone — before spatial encoding	4	Directly from a mic (Zoom H3-VR, Ambeo, Rode NT-SF1, …). Must be converted before use in a DAW.
B-Format FOA	First-Order Ambisonics scene — 4 spherical harmonic channels	4	Entry-level recordings, simple setups, older archives
B-Format HOA-3	Third-Order Ambisonics — finer spatial resolution	16	Zylia ZM-1 microphone output, intermediate productions
B-Format HOA-7	Seventh-Order Ambisonics — maximum spatial resolution	64	ICST studio standard, large speaker arrays, high-quality archiving
FuMa legacy	Older channel ordering and normalisation convention (W, X, Y, Z / MaxN)	4–36	Older plugins, historical archives, some first-order workflows
ambiX ICST standard	Modern convention: ACN channel ordering + SN3D normalisation	4–64	All current ICST, IEM, SPARTA, and most modern HOA tools

A-Format vs B-Format

	A-Format	B-Format
What it contains	Raw capsule signals (microphone-specific)	Spatial sound-field representation (spherical harmonics)
Channels (1st order)	4	4 (FOA) up to 64 (HOA-7)
Transferable between tools?	No — tied to the microphone model	Yes — standard exchange format
Can be decoded directly?	No — must be encoded to B-Format first	Yes — feeds decoder or binaural renderer directly
Typical source	Ambisonic microphone output	DAW B-Format bus, archive file, encoder output

Practical rule: A-Format comes from the microphone and must be converted first. B-Format is the spatial scene you route, decode, archive, and render.

FuMa vs ambiX

	FuMa legacy	ambiX ICST standard
Channel ordering	FuMa (W, X, Y, Z, …)	ACN (0, 1, 2, 3, …)
Normalisation	MaxN	SN3D
Supported orders	Mainly 1st order (some tools up to 3rd)	All orders up to HOA-7 and beyond
Where you see it	Older plug-ins (e.g. classic Ambisonic Toolkit versions, legacy archives)	ICST, IEM, SPARTA, REAPER, modern export pipelines
File format	WAV (standard multichannel)	WAV or RF64 (for files > 4 GB)
ICST recommendation	Only when a tool specifically requires it	✓ Use by default

If in doubt: choose ACN / SN3D — that is ambiX, and it is what every current ICST tool expects.

Orders & Channel Counts

The number of channels in a B-Format signal is determined by the Ambisonics order:

channels = (order + 1)²

Order	Name	Channels	Spatial resolution	Typical use
1	FOA	4	Basic	Entry-level recording, simple setups, most Ambisonic microphones
2	HOA-2	9	Moderate	Intermediate compositions, some older HOA tools
3	HOA-3	16	Good	Zylia ZM-1 output, standard HOA productions
4	HOA-4	25	High	Research, large arrays
5	HOA-5	36	Very high	Eigenmike em32, large dome setups
6	HOA-6	49	Very high	Specialised research applications
7	HOA-7	64	Maximum	ICST studio standard — 64-channel B-Format bus in REAPER

In REAPER, the ICST workflow uses a 64-channel B-Format bus. This ensures that no HOA channels are silently lost, regardless of which order you are working in.

Normalisation Conventions

Normalisation defines how the amplitude of each spherical harmonic component is scaled. Using the wrong convention between encoder and decoder produces incorrect spatial rendering — even if the channel order is right.

Convention	Full name	Used in	Notes
SN3D ICST standard	Schmidt Semi-Normalised 3D	ambiX, ICST, IEM, SPARTA, most modern HOA tools	De-facto standard for production and exchange. Use this.
N3D	Full 3D Normalised	Some research tools, mathematical contexts	Differs from SN3D by a constant factor per order. Common in academic literature.
MaxN legacy	Maximum Normalised	FuMa convention	Normalises each component to its peak value. Used in older systems and archives.

ICST Recommendation

For all new Ambisonics work:
Use ambiX — ACN channel ordering + SN3D normalisation.

In REAPER: route through a 64-channel B-Format bus.
Decode only at the monitoring or final rendering stage.

This keeps your session open: the same B-Format master can feed loudspeaker decoding, binaural monitoring, archive export, and later rendering for any playback system.

Go deeper: Ambisonics Formats Explained — the full technical reference with all conventions, ACN numbering, and archiving guidelines.

Back to: Ambisonics 101