The ICST Ambisonics Decoder

Institute for Computer Music and Sound Technology / (ICST) Zurich University of the Arts

The ICST Ambisonics plug-ins are based on the first Ambisonics plug-ins written together with Dave Malham in 2003 and extended in 2004. They contain all the essential functions of the ICST Max Externals and are available in VST3, AU and VST3 for Windows formats. Version 2.0 (2020) plug-ins are available as universal 64-bit binaries:

AmbiDecoder plug-ins 1st to 7th order.
AmbiEncoder plug-ins 1st to 7th order with mono input (one channel)
AmbiEncoder plug-ins 1st to 7th order with multiple inputs (up to 64 channels)

The ICST Ambisonics Decoder expects a B-format in AmbiX format as input signal. (1. The Ambisonics formats FuMa and AmbiX ). Depending on the Ambisonics order, it requires a different audio channel routing. The B-format signals (WXYZ) describe what the listener should hear. But how these signals are distributed to the different speaker arrays (settings) is the task of the Ambisonics decoder. If the decoder knows the orientation (A,E,D) of each loudspeaker, almost any set-up can be decoded. The ICST Ambisonics Decoder can be used for symmetrical as well as asymmetrical speaker settings.

The facts are here: Specifications AmbiDecoder v2.2

ICST Ambisonics Decoder Viewing-Layers

The first layer of the ICST Ambisonics Decoder at a glance: Layer 01 (Loudspeaker Settings)

The speaker settings layer combines all necessary parameters for the speaker settings and its management.

Figure 01: Decoder view in the first layer: Loudspeaker mode

A: Edit mode:

In the Edit mode of the ICST Ambisonics Decoder, the loudspeaker coefficients are entered.

Use the "Distance scaler" (C) to enter the room size, measured from the centre.
Measure each speaker in its position azimuth, elevation, distance (AED) or in (XYZ). Enter these coordinates in the decoder (A). (double-click in the "Value" field) or load a preset.

Figure: 02: Loudspeaker coefficients entered.

Presets: load (default)

2 (stereo)
4 (quadro)
6 (hexagon)
8 (octagon)

Save Presets

Save your own speaker settings
The speaker presets are saved in XML format.

Preset Manager:

Import Export remove -->Presets

Figure 03: Speaker Preset Manager

B: In section (B), the audio gain and filters are available.

In this way, the bass, for example, can be cut for each speaker in no time at all.

Figure 04: Filter manager of the ICST AmbiDecoder

Under "manage filters" the filter presets can be managed.
The filter settings can be saved as presets.

Figure 05: Shows the audio section of the ICST Ambisonics Decoder.

Click on the "?" symbol and the help window opens.

For the sound check, a noise generator is available for adjusting the loudspeakers.
This allows you to adjust the loudness of each loudspeaker individually. (click on the loudspeaker symbol)

Or "press --> Test all speakers" to test the speakers one after the other with a white noise.

Figure 06: Test all speakers with white noise.

C: Channel weights: The following weights can be selected:

Ambisonics weighting selection (A).

Basic: Sets all weights to 1
In-Phase: The weighting of the Ambisonics channels is based on the order of the channels. calculate in phase
Manual: The weights of each Ambisonics dimension can be changed individually with the sliders

Distance scaler: Defines the room length in metres (B)
In manual mode, the user can set the weights himself. (C)