ICST AmbiDecoder – Multi-Decoder Mode
Institute for Computer Music and Sound Technology / (ICST) Zurich University of the Arts
Multi-Decoder Mode
The Multi-Decoder Mode, introduced in ICST AmbiDecoder v3.2, allows you to run up to four fully independent decoders within a single plugin instance. This is ideal for complex loudspeaker setups that combine different speaker arrays — for example, a main Ambisonics ring together with height speakers, a subwoofer group, or a separate near-field array.
When to use Multi-Decoder Mode
Use Multi-Decoder Mode when your setup includes:
- Multiple speaker layers (e.g. horizontal ring + height dome)
- Mixed-order decoding (e.g. 3rd order for horizontal, 1st order for height)
- Different speaker geometries that require separate presets
- Independent gain and filter settings per group of loudspeakers
For straightforward setups (single array, single geometry), the standard single-decoder mode is sufficient.
Activating Multi-Decoder Mode
- Open the ICST AmbiDecoder plugin in your REAPER FX chain.
- In the Decoder Settings panel, locate the Multi-Decoder toggle.
- Enable Multi-Decoder Mode — four decoder slots (A, B, C, D) will appear.
[!Tip:] Each decoder slot is fully independent and can be configured separately without affecting the others.
Configuring Each Decoder
For each of the four decoders, you can set:
1. Name and Color
- Give each decoder a descriptive name (e.g. “Ring”, “Height”, “Sub”, “Near”).
- Assign a custom color for easy identification in the UI.
2. Loudspeaker Selection
- Each decoder has its own speaker selection.
- Assign specific speakers from your loudspeaker preset to each decoder.
- Speakers can only belong to one decoder at a time.
3. Ambisonics Order
- Set the decoding order independently per decoder (1st to 7th order).
- Lower orders (1st–2nd) are suitable for sparse or difficult speaker geometries.
- Higher orders (3rd–7th) give more precise localisation for dense arrays.
4. Ambisonics Weighting
- Choose the weighting scheme (e.g. MaxRe, inPhase, Basic) per decoder.
- MaxRe is recommended for most practical setups.
5. Filters
- Eight filter options are available per decoder.
- Adjust per-decoder EQ and spatial filtering independently.
6. Mute and Gain
- Each decoder has an independent mute button and gain control.
- Use mute to isolate individual decoders during setup and testing.
Routing in REAPER
When using Multi-Decoder Mode, the plugin still receives the same B-Format master bus as input. The routing within the plugin distributes the signal to each decoder internally.
Output channels are assigned sequentially:
- Decoder A → Outputs 1–N (based on its speaker count)
- Decoder B → Outputs N+1–M
- Decoder C → continues after B
- Decoder D → continues after C
Make sure your REAPER track has enough output channels configured to cover all speakers across all four decoders.
[!Attention:] Check your track channel count and routing carefully. Missing channels will result in silent speakers without any error message.
Speaker Testing
To verify each decoder:
- Mute decoders B, C, and D.
- Click Speaker Test on decoder A and step through its speakers.
- Repeat for each decoder after unmuting it.
Use Shift + Control + S / Shift + Control + M (macOS) for keyboard-based solo and mute during testing.
Example: Horizontal Ring + Height Dome
A common multi-decoder use case at ICST is an Oktagon ring (8 speakers, horizontal) combined with a height layer (4 elevated speakers):
| Decoder | Speakers | Order | Weighting |
|---|---|---|---|
| A | Ring (1–8) | 3rd | MaxRe |
| B | Height (9–12) | 1st | MaxRe |
This setup allows fine-tuned decoding for each layer independently, with separate gain compensation for the height speakers.
Further Resources
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