ICST Ambisonics Workshop: Working with Ambisonics

johannes.schuett@zhdk.ch (Johannes Schuett) — Sun, 03 May 2026 00:00:00 +0000

Working with Ambisonics

Online-Workshop · ICST / ZHdK · ambisonics.ch

Online Course Self-paced Zylia ZM-1 ICST Plugins HOA 3rd Order Reaper pre-installed

🎛️ REAPER + ICST AmbiEncoder/Decoder 🎙️ Zylia ZM-1 (16-channel HOA) 🔄 FuMa ↔ AmbiX Conversion

Learning Objectives

After this workshop you will be able to:

explain the Ambisonics signal flow from recording to playback
distinguish A-format (PCM audio) from B-format (mathematical format)
set up and route a Zylia ZM-1 HOA recording in Reaper
position sound sources in three-dimensional space using the ICST AmbiEncoder_64
convert FOA/HOA material between FuMa and AmbiX formats
carry out a guided hands-on exercise (Encoding → Mixing → Decoding) independently
integrate external tools (MaxMSP, Csound/Cabbage) into an Ambisonics workflow

📋 Preparation Reaper is pre-installed on all workshop computers (v7+, incl. ICST plugins) · Bring headphones (binaural monitoring) · Download the large workshop package (Reaper folder + papers) in advance

A Overall Workflow B Recording C Reaper Workflow D External Tools E Csound F MaxMSP G Discussion

BLOCK A

Overall Workflow

Signal FlowFormatsHOA Orders

Ambisonics is a channel-format-independent, full-sphere audio system. Every production follows the same chain — regardless of whether the target is headphones, an 8-channel ring, or a 24-channel dome.

The Ambisonics Signal Flow

Ambisonics signal flow: From recording (A-format → B-format ambiX) through the HOA bus and production to the three output formats — B-format master, binaural stereo, and array/live.

Step	What happens	Tool (Workshop)
1. Recording	Microphone array → A-format (raw capsules) or direct HOA	Zylia ZM-1 → Zylia App
2. A-to-B Conversion	Raw capsule data → B-format (AmbiX / HOA)	Zylia App, JS plugin
3. Encoding	Position mono/stereo sources in space	ICST AmbiEncoder_64
4. Processing	EQ, reverb, panning on the HOA bus	Reaper FX chain
5. Decoding	B-format → playback format	ICST AmbiDecoder
6. Delivery	Render master, choose format	Reaper Render

The golden rule: Render the B-format master track — never the decoder output. The decoder is for monitoring only. One and the same B-format master works for headphones, loudspeakers, and streaming.

📖 Further reading: Ambisonics Fundamentals → Ambisonics in 30 Minutes — compact overview of the system
→ Workflow from Recording to Delivery — in-depth step-by-step guide
→ Getting Started: ICST Plugins in Reaper — introduction to the plugin chain

Monitoring Setup

Before recording starts, monitoring must be in place:

Binaural (headphones): Load ICST AmbiDecoder with HRTF preset → direct spatial feedback without loudspeakers
Check decoder preset: Does the layout (channel count, speaker geometry) match the actual setup?
Never run binaural and loudspeakers in parallel: Only one decoder active — otherwise phase errors in the mix
Separate monitoring branch: Binaural monitor track on a dedicated bus, not looped into the B-format master

📖 Further reading: Binaural Monitoring → Binaural Monitoring in the ICST Workflow — HRTF setup, decoder presets, monitoring practice

Formats & Normalisation

Format	Channel order	Normalisation	Status
FuMa (Furse-Malham)	W, X, Y, Z	MaxN	Older, legacy
AmbiX (ACN / SN3D)	W, Y, Z, X	SN3D	Current standard

Rule of thumb: Always work and archive in AmbiX (ACN/SN3D). Use FuMa only for compatibility with legacy material.

HOA Order	Channels	Microphone example	Spatial resolution
1st Order (FOA)	4	Zoom H3-VR, Sennheiser Ambeo	Good as stereo replacement, coarse directionality
2nd Order	9	—	Significantly sharper localisation
3rd Order	16	Zylia ZM-1	High resolution, production reference

📖 Further reading: Formats & Orders → Ambisonics Formats Explained — FuMa, AmbiX, ACN, SN3D in detail
→ Which Ambisonics Order Do I Need? — practical decision guide

Delivery Formats

Target	Format	Note
Archive / Master	Multichannel WAV, AmbiX, 48 kHz / 32-bit float	Unaltered B-format master
Binaural	2-channel WAV	Streaming, preview, headphones
Loudspeakers	N-channel WAV	Performance, installation
YouTube 360	Binaural + Spatial Metadata	Spatial Media Metadata Tool

📖 Further reading: Exporting B-Format → Render B-Format in REAPER — step-by-step render setup
→ Exporting the B-Format Master — Reaper settings for archive and delivery

BLOCK B

How to Record Ambisonics — Zylia ZM-1

Microphone SetupA-to-B ConversionReaper Session

Recording 3D Audio: The Recording Workflow

From capsule to B-format: microphone array (A-format, raw capsules) → A-to-B conversion in the Zylia app → 16-channel B-format (AmbiX). All three stages are covered in the workshop workflow.

Workflow (Hands-on with Zylia → Main Reaper)

Short Recording Session — Set up Zylia ZM-1, check levels (−18 dBFS), record 30–60 seconds → 19-channel A-format PCM
A to B Converting — Zylia App: import A-format, export as 3rd Order HOA → 16-channel B-format AmbiX WAV
A-format = PCM audio (regular audio data, raw capsules)
B-format = Mathematical format (spherical harmonics, not directly listenable)
Listening B-Format — Load in Reaper, listen binaurally via HOA bus + AmbiDecoder: does "front" actually sound in front?
Upsampling & FX — EQ, reverb on HOA bus, distance automation on the encoder
Mastering B-Format — Render HOA Render Bus: 16 ch, 48 kHz, 32-bit float WAV → B-format master

💡 Thunderstorm Example (Zylia Recording) A thunderstorm recording shows why HOA far surpasses stereo: thunder comes from all directions (full envelopment), rain falls from above (elevation), wind rotates (rotation of the sound field). In stereo: just a left-right smear. In Ambisonics: a complete sphere.

Microphone Specifications

19-capsule array (omnidirectional)
Output: 19 raw channels → encoded to 3rd Order HOA (16 channels, AmbiX) by the Zylia software
Connection: USB-C, no external power required

Microphone Placement

The position of the microphone determines the listening perspective — this is not a technical but a compositional decision.

Height: approx. 1.5 m for a natural ear-level perspective; lower for a “ground level” effect, higher for an overview perspective
Orientation: The microphone has a preferred direction (marker). “Front” in B-format corresponds to this direction — document it so that decoding is correct
Distance to source: Closer = more direct sound, more spatial detail; further = more diffuse field, less localisation
Reflections: Hard walls, floors, and ceilings are very prominent in an HOA microphone — listen carefully to the placement location before recording
Wind protection: Always use a windshield outdoors (blimp or fur). Activate LF roll-off below 80 Hz

Gain Management

Target level: approx. −18 dBFS (check all 19 channels individually)
Headroom: at least 12 dB — transients in HOA microphones can peak unexpectedly
Monitor all raw channels separately: a single clipping channel corrupts the entire B-format
Set the gain structure in the Zylia app, not in Reaper after the fact

A-to-B Conversion

The Zylia ZM-1 delivers A-format (19 raw channels). The Zylia software converts these to 3rd Order HOA (16 channels, AmbiX):

When to convert? Immediately after recording, before importing into Reaper
Quality control: Test phase and channel assignment — a mono test source from the front should sound clearly in front in the binaural monitor
Archive raw data: Always keep the A-format (19 channels) — this allows re-conversion later with better software

📖 Further reading: A-format & B-format → Recording with an Ambisonics Microphone – A-format, B-format — conversion workflow and quality control explained

Field Recording Checklist

Before recording:

Acoustic survey: reflections, noise sources, wind direction
Decide on microphone placement and document it (height, orientation, distance)
Level check: all 19 channels at approx. −18 dBFS
Binaural monitoring active and verified
Metadata template prepared (location, date, take number, weather)

After recording:

A-to-B conversion in Zylia app
Load HOA file (16 ch AmbiX) in Reaper and verify binaurally
Archive raw channels (A-format)

Reaper Session (pre-configured)

Track	Channels	Function
Notes	—	Notes track (muted)
Zylia ZM-1	16	Armed for recording · VU: multichannel peaks
HOA Bus	16	AUXRECV from Zylia · no direct out
ICST AmbiDecoder	18	16 ch in + 2 aux · decoder plugin
Binaural Monitor	2	Headphone monitoring
HOA Render Bus	16	Muted · for offline render

📥 Download: Pre-configured Reaper Session All tracks, routing, and decoder preset are pre-configured — just open and start.
→ zylia_recording_example.RPP

📖 Further reading: Room Recording & Acoustics → Capturing Space and Synthetically Creating Space — room acoustics and recording technique for HOA productions

Common Recording Errors and Solutions

Problem	Cause	Solution
Sound seems “back to front”	Microphone orientation not documented	Test and note front/back on location
Comb filtering / unstable direction	Faulty A-to-B conversion	Check for spectral artefacts, repeat conversion
Clipping on individual channels	Overloading of individual capsules	Monitor all 19 raw channels separately, reduce gain
Wind noise in low frequencies	Missing wind protection	LF roll-off below 80 Hz, use blimp
No elevation	FOA loaded instead of HOA	Check channel count: FOA = 4 ch, HOA 3rd = 16 ch
B-format import in Reaper incorrect	Wrong ordering (FuMa instead of AmbiX)	Use FuMa → AmbiX converter (JSFX, Block C)

Composers Workflow — The Three Stages

The paradigmatic workflow of the Ambisonics Toolkit: Author → Image → Monitor. Every Ambisonics production passes through the same three stages — regardless of tool and output format.

Every Ambisonics production — whether field recording, synthesiser, or live performance — passes through three stages:

Stage	Question	In practice
Encoding	Where is the sound in 3D space?	Azimuth, elevation, distance — via ICST AmbiEncoder_64 or Lua script
Processing	How does the sound move and how does it interact with the space?	Rotation, movement automation, reverb on HOA bus, distance simulation
Decoding	How do I play this back on my audio system?	ICST AmbiDecoder: binaural (HRTF), loudspeaker ring, MultiDecoder

Complete signal flow of an Ambisonics production environment: external tools (AbletonLive, Csound, SuperCollider, Max 9) → bridges → DAW (sound design, spatialisation, mix & mastering) → B-format → decoding. OSC/MIDI connects all layers.

BLOCK C

Reaper Workflow: Encoding · Processing · Decoding

ICST AmbiEncoder_64Lua AutomationDecoding

Encoding with ICST AmbiEncoder_64

Plugin: ICST AmbiEncoder_64 (VST3) — pre-installed on all workshop computers.

Parameter	Index	Normalised	Meaning
Azimuth	11	0–1 → −180° to +180°	Horizontal position
Elevation	12	0–1 → −90° to +90° (0.5 = horizon)	Vertical position
Distance	13	0 = near · 1 = far	Depth

📥 Lua script: Encoding example → icst_ambi_encoding_voice.lua — sets track, loads AmbiEncoder, positions source at azimuth −45°, elevation +20°

📖 Further reading: ICST AmbiEncoder → ICST Encoders — all parameters, modes, and encoder variants at a glance
→ ICST AmbiEncoder – Spiral Walk Script — example of complex Lua automation
→ ICST AmbiEncoder – OSC Syntax — control the encoder via OSC (Touchdesigner, Max, etc.)

Automation: Moving Sound Sources

Physik-basierte Trajektorie: atan2 für Azimut, √(x²+y²) für Distanz.

📥 Lua scripts: Train pass-by → icst_ambi_zug_langsam.lua — slow train, 28 seconds
→ icst_ambi_zug_schnell.lua — express train, 4 seconds
→ icst_ambi_zug_vergleich.lua — pause + slow + pause + fast in sequence

Processing

Distance

In the ICST AmbiEncoder, Param 13 (Distance) simulates depth in space. The plugin attenuates level and high-frequency content with increasing distance — similar to air absorption in real space:

Near sources (distance ~0): present, direct, high HF content
Distant sources (distance ~1): quieter, duller, more diffuse-field content
Combined with reverb: The greater the distance, the higher the wet amount in the room plugin on the HOA bus

📥 Reaper example: Distance automation → icst_stereo_pan_distanz.lua

Room / Reverb

The reverb sits on the HOA bus track — not on the source track. Only then does the reverb remain anchored in Ambisonics space and get decoded correctly with the B-format.

ReaVerb or FX reverb on the HOA bus (after all encoders, before the decoder)
Dry/wet ratio: start sparingly (~10–20% wet), as HOA reverb sounds very prominent
Room size and pre-delay determine the size of the space
Separate reverb sends per source allow different room distances

📥 Reaper example: Room curves → icst_stereo_pan_raumkurven.lua

Example: Helicopter Flyover

Phase	Azimuth	Elevation	Distance
Approach (front)	~0°	15° → 70°	1.0 → 0.3
Overhead	0° → 180°	70° → 85° → 70°	0.3 → min → 0.3
Departure (rear)	~180°	70° → 15°	0.3 → 1.0

The script calculates position, azimuth, and elevation directly from 3D coordinates (atan2, Pythagoras) — no manual angle estimation.

📖 Further reading: Spatial Parameters → Spatial Parameters as Compositional Material — creative use of azimuth, elevation, and distance

📥 Lua script: Helicopter flyover → icst_ambi_kopter.lua — 18 s flyover, 360 points, configurable height and lateral offset

Decoding

Binaural: ICST AmbiDecoder with HRTF file → 2-channel headphones
Loudspeakers: Decoder with .spk configuration file
Screensets: Ctrl+Alt+1 (Recording) · Ctrl+Alt+2 (Mixing) · Ctrl+Alt+3 (Decoding)

📖 Further reading: Decoding & Delivery → ICST AmbiDecoder – Multi-Decoder Mode — running multiple output formats in parallel
→ Binaural Rendering and Headphone Delivery — binaural render for streaming and headphones

FuMa → AmbiX Conversion (FOA)

For legacy material in FuMa format (e.g. SoundField, older productions):

FuMa Input	AmbiX Output (ACN)	Gain correction
Ch1 = W	ACN 0 = W	× √2 = +3.01 dB
Ch2 = X	ACN 3 = X	× 1/√3 = −4.77 dB
Ch3 = Y	ACN 1 = Y	× 1/√3 = −4.77 dB
Ch4 = Z	ACN 2 = Z	× 1/√3 = −4.77 dB

📥 JSFX plugin + Lua installer → FuMa_to_AmbiX_FOA.jsfx — JSFX plugin
→ icst_fuma_to_ambix_foa.lua — Lua installer
In Reaper: Actions → Load new Script → icst_fuma_to_ambix_foa.lua

BLOCK D

External to Reaper

MaxMSPCsoundMax for Live

Reaper is not the only environment for Ambisonics. These tools are used by composers and researchers — each with a different approach and different strengths.

Workflow with MaxMSP: ICST Ambisonics Externals (ambicontrol, ambiencode, ambidecode). Real-time spatialisation, OSC control of the ICST AmbiEncoder in Reaper. Strength: generative and algorithmic spatialisation, live electronics.

Workflow with Csound (Cabbage.app): Csound opcodes bformenc1 / bformdec2. Cabbage wraps Csound as a VST3 plugin. Strength: precise mathematical control of the sound field, additive synthesis, granular synthesis.

Workflow with Max for Live: MaxMSP integrated in Ableton Live. Combines Ableton’s production workflow with Ambisonics spatialisation. Strength: live performance with Ambisonics, studio production.

📌 Note Blocks D, E, and F go beyond the 4-hour workshop scope. They are introduced here as an overview and explored in depth in a follow-up workshop.

BLOCK E

Csound / Cabbage

Additive SynthesisSpatialisationVST3

Csound is a programmable audio synthesis language. Cabbage wraps Csound instruments as VST3 plugins and makes them usable in Reaper.

Cabbage → Reaper (DAW)

Integration of Cabbage/Csound into Reaper: Cabbage.app sends audio to Reaper via BlackHole_64 (virtual audio interface). OSC enables bidirectional communication — Reaper can control spatialisation parameters, Csound can receive encoder positions.

Key Csound opcodes for Ambisonics:

bformenc1 — encodes a mono signal into B-format (1st–3rd order). Input: audio, azimuth, elevation. Output: HOA channels.
bformdec2 — decodes B-format to a loudspeaker array.

Example: Additive Synth & Random Spatialisation (Cabbage)

A Cabbage example demonstrates: an additive synthesiser generates partials (sine waves) in real time. Each partial is independently spatialised with bformenc1 and a randomised azimuth/elevation. The position drifts randomly — the result is a moving cloud of sound in 3D space, then decoded binaurally.

BLOCK F

MaxMSP — ICST Ambisonics Externals

ACT-ToolOSCReal-time

MaxMSP with the ICST Ambisonics Externals provides a complete real-time Ambisonics environment. Unlike a DAW, Max allows algorithmic and generative control of spatialisation — positions can be driven by data, gestures, sensors, or other audio signals.

MaxMSP → Reaper (DAW)

MaxMSP and Reaper communicate via BlackHole_64 (audio), OSC (spatialisation parameters), and MIDI. Max9 can control the ICST AmbiEncoder in Reaper in real time — azimuth, elevation, and distance as live automation.

ICST Ambisonics Externals:

ambiencode~ — encodes mono audio into B-format. Message input for azimuth, elevation, distance.
ambidecode~ — decodes B-format to loudspeakers or binaural.
ambicontrol — GUI panel for manual spatialisation control.

ACT-Tool Example:

The ACT-Tool (Ambisonics Composition Tool) is a MaxMSP patch developed at ICST:

3D visual interface for placing and animating sound sources
Sources can be moved manually (mouse/trackpad) or algorithmically (LFOs, envelopes, data streams)
OSC output: sends azimuth, elevation, and distance to any Ambisonics encoder — including the ICST AmbiEncoder in Reaper
The ACT-Tool can be used as a “spatial score”: define movement visually, record OSC output as automation in Reaper

Hands-on Exercise

Guided exercise with the prepared sessions:

Open the Zylia session, verify microphone routing and decoder preset
Route a mono test source to the HOA bus, listen binaurally
Run the encoding script: position source at azimuth −45°, elevation +20°
Start the train pass-by automation and follow the trajectory binaurally
Encode your own source and move it in space (automation or manually)
Render and verify the B-format master (16 ch, not 2 ch!)

📖 Further reading: Compositional Practice → Spatial Counterpoint — spatial contrary motion as a compositional technique
→ Reaper Ambisonics Setup in 20 Minutes — quick setup for your own projects after the workshop

BLOCK G

Composer Discussion

TopicsQ&AOutlook

A guided discussion to consolidate the workshop experience. Not a lecture — participants share their own observations and develop ideas together.

Topics:

Space as compositional material: Can space itself be the instrument? What happens when the space moves and the source stays still?
The composer’s perspective: How does working in Ambisonics change compositional decisions compared to stereo?
Elevation and expressivity: When does height feel natural, when artificial? What does the vertical axis enable that stereo never could?
Distance and reverb: How do distance and reverb interact? When does a source sound “inside the space” rather than “outside”?
Outlook — follow-up workshop: MaxMSP + Csound in depth (Blocks D, E, F).

Preparation & Downloads

Reaper is pre-installed on all workshop computers (v7+, incl. ICST plugins)
Bring headphones (binaural monitoring)
Download the pre-configured Reaper session in advance

⬇ ICST Workshop — Large Download (pCloud)Pre-configured Reaper folder (drag in Reaper.app → ready to go) + Workshop papers ⬇ ICST_Ambisonics_Workshop_2026.zipComplete workshop package — Reaper session, Lua scripts, Csound, MaxMSP (6.8 MB) zylia_recording_example.RPPPre-configured Reaper session for Zylia ZM-1 Workshop Document (.docx)Complete workshop document icst_ambi_encoding_voice.luaEncoding: voice at Az −45°, El +20° icst_ambi_zug_langsam.luaSlow train pass-by (28 s) icst_ambi_zug_schnell.luaExpress train pass-by (4 s) icst_ambi_zug_vergleich.luaTrain comparison (slow + fast) icst_ambi_kopter.luaHelicopter flyover (3D, 18 s) FuMa_to_AmbiX_FOA.jsfxFuMa → AmbiX FOA Converter (JSFX) icst_fuma_to_ambix_foa.luaFuMa → AmbiX Lua installer ICST B-Format ArchiveArchive with HOA example files to explore Best PracticesRecommendations for professional Ambisonics productions

Fuma on ICST Ambisonics