Ambisonics Formats at a Glance
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 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.
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