Ambisonics

Full-sphere audio capture and reproduction technology.

Principle

Ambisonics encodes the soundfield rather than discrete channels. This encoding can then be decoded for any speaker layout.

Recording ──► Encoding ──► B-Format ──► Decoding ──► Speakers
                              │
                              └──► Any configuration

Spherical Harmonics

Ambisonics decomposes the soundfield into spherical harmonic components:

Order	Components	Description
0	W	Omnidirectional (pressure)
1	X, Y, Z	Three figure-8 (velocity)
2	5 components	Finer directional detail
3	7 components	Even finer detail

Ambisonic Orders

First Order Ambisonics (FOA)

4 channels (W, X, Y, Z):

• Minimum viable Ambisonics
• ~45° angular resolution
• Compatible with 4+ speakers

Higher Order Ambisonics (HOA)

More components = better resolution:

Order	Channels	Angular Resolution
1	4	~45°
2	9	~30°
3	16	~22°
4	25	~18°
5	36	~15°

Channel count formula: (order + 1)²

Formats

B-Format (Legacy)

Original Ambisonic format:

• Channel order: W, X, Y, Z
• FuMa normalization
• Still used in some software

AmbiX (Standard)

Modern standard:

• ACN channel ordering
• SN3D normalization
• Used by YouTube 360, Facebook 360, VR

Channel Order Comparison

Channel	B-Format	AmbiX (ACN)
0	W	W
1	X	Y
2	Y	Z
3	Z	X

Recording

Soundfield Microphone

Tetrahedral array of 4 capsules:

• Captures first-order B-format
• Examples: Sennheiser Ambeo, Zoom H3-VR

Higher Order Capture

More capsules for higher orders:

• Eigenmike: 32 capsules, up to 4th order
• Zylia ZM-1: 19 capsules, 3rd order

Virtual Sources

Create Ambisonic content from mono sources:

• Encode mono at specific direction
• Mix multiple encoded sources
• Full creative control

Decoding

Basic Decoding

Simple matrix multiplication to speaker feeds:

speaker_gains = decoder_matrix × ambisonic_signals

Decoder Types

Type	Characteristics
Basic	Simple, can have level variations
Max-rE	Optimized for diffuse field
In-phase	No negative coefficients
Dual-band	Different decoders for low/high freq

Binaural Decoding

Decode to headphones using HRTF:

• VR/AR applications
• Personal listening
• Preview/monitoring

Advantages

• Format independent: Same content works on any system
• Rotation: Easy to rotate entire soundfield
• Scalable: Trade quality for channel count
• Future proof: Decode to systems not yet invented

Limitations

• Complexity: More complex than channel-based
• Order vs speakers: Need enough speakers for the order
• Sweet spot: Decoding optimized for center
• Bass management: Requires special handling

Software

Production

• Reaper with Ambisonic plugins
• IEM Plugin Suite (free)
• Spatial Audio Designer

Decoding

• Ambidecoder
• IEM AllRADecoder
• Platform-native (YouTube, Facebook)

Ambisonics and Spacelite

While Spacelite doesn't directly process Ambisonics, it can:

• Work downstream of Ambisonic decoding
• Complement Ambisonic systems for coverage extension
• Handle subwoofer management for Ambisonic speakers

The HSR and Ambisonics both aim for flexible, scalable spatial audio, but with different approaches:

• Ambisonics: Full soundfield, any configuration
• HSR: Stereo to multichannel, preserving original image