ICST Decoder

kannst du mir Institute for Computer Music and Sound Technology (ICST) · Zurich University of the Arts

ICST Ambisonics Decoder

Decoding is the central interface between the Ambisonics B-format and physical loudspeaker reproduction – its quality determines spatial precision, depth layering, and localization.

While binaural playback over headphones is today largely mature through established plug-ins (e.g., IEM, SPARTA), decoding for real loudspeaker arrays remains a technically and psychoacoustically demanding task. Geometry, delay times, weightings, filtering, and Ambisonics order must all be precisely coordinated.

The ICST Ambisonics Decoder is a powerful, practical tool developed specifically for flexible loudspeaker setups in studio and live contexts. In addition to standard configurations (e.g., Quadro, Octagon, 7.1.4), asymmetric or individually measured loudspeaker arrangements can also be accurately mapped.

The decoder was developed in the context of the ZHdK’s 3D Composition Studio and has been continuously tested in studio and concert operation. The goal was to provide a flexible, reproducible, and sonically transparent decoding system for Higher-Order Ambisonics workflows.

Plugin Formats

The ICST Ambisonics Decoder Plugins are available as:

• VST3
• AU (Component)
• LV2 (experimental – not recommended for production use)

Wiki: ICST AmbiDecoder · schweizerweb/icst-ambisonics-plugins Wiki · GitHub

All examples in this article are performed in REAPER. REAPER supports up to 128 audio channels per track and is therefore particularly well-suited for Higher-Order Ambisonics productions.

Overview ICST Ambisonics Decoder

Main Areas of the User Interface

1. Radar – horizontal view of the loudspeaker arrangement (ICST Composition Studio)
2. Vertical radar view (Z-axis)
3. Speaker parameters
   • CH = Index
   • Name = loudspeaker label
   • Coordinates: Cartesian (XYZ) & Polar (Azimuth, Elevation, Distance)

Settings & Help

4. Gear icon → Opens the Speaker Settings window
5. Question mark → Help window

Speaker Parameter Editor:

Keyboard Shortcuts

Workflow: Ambisonics Decoding in REAPER

Recommended Track Structure

Create three 64-channel audio tracks in REAPER:

1. B-Format Source Track – 1st–7th Order Ambisonics file
2. Ambisonics Bus – collects multiple B-format signals, hosts mastering FX
3. Decoder Track – hosts the ICST Ambisonics Decoder, output to loudspeakers

This clear separation ensures transparency, modularity, and reproducible setups.

ICST AmbiDecoder – Step-by-Step Setup

1. Add the ICST AmbiDecoder plugin to the Decoder Track.

   

   By default the decoder opens with the Stereo (90°) setting.

   

2. Open the Speaker Settings window (gear icon → “Speaker”). Select one of the many standard presets or enter your own loudspeaker configuration.

   

3. Optionally activate the Filter section to equalize individual loudspeakers.

   

   Available filter types per speaker:

   

   📋 To Do

   Add screenshot: measured loudspeaker setup of the ICST Composition Studio

4. Under “Speakers” edit the speaker parameters directly and save them as a preset.

   

5. Under “Ambisonics” select the desired order (up to 7th order) and Channel Weights.

   

6. Scale room dimensions as needed – loudspeaker coordinates and delay times are recalculated automatically.

   

Audio Test Function

The decoder features an integrated test section:

• Pink noise generator
• Individual test per loudspeaker
• Sequential test of all loudspeakers clockwise (“Test all speakers”)
• Mute / Solo via Ctrl + Shift + M / Ctrl + Shift + S

This enables a quick technical check of the entire system before rehearsal or performance.

Save & Load Presets

Speaker configurations can be saved as presets and reloaded at any time. This ensures reproducibility across sessions and venues.

Summary

The ICST Ambisonics Decoder offers:

• Precise Higher-Order Ambisonics decoding
• Flexible loudspeaker geometries (symmetric & asymmetric)
• Per-speaker filtering and equalization
• Integrated test and measurement functions
• Multi-layer MultiDecoder architecture
• Preset management for reproducible setups
• Seamless integration into professional DAW workflows

It thus forms a robust foundation for artistic, scientific, and production-oriented applications in 3D audio.