ICST AmbiDecoder – Multi-Decoder Mode

• 2025-11-10
• 4-minute read
• intermediate

Multi-Decoder Mode

Level: Advanced | Audience: Technician, Studio engineer.

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

1. Open the ICST AmbiDecoder plugin in your REAPER FX chain.
2. In the Decoder Settings panel, locate the Multi-Decoder toggle.
3. Enable Multi-Decoder Mode — four decoder slots (A, B, C, D) will appear.

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.
• Use filters carefully and for clear reasons.
• In many cases, small layer-specific corrections are more useful than strong spectral reshaping.
• A height layer may benefit from slightly different spectral treatment than the main ring, but this should always be verified by listening on the real array.

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.

Speaker Testing

To verify each decoder:

1. Mute decoders B, C, and D.
2. Click Speaker Test on decoder A and step through its speakers.
3. Repeat for each decoder after unmuting it.

Use Shift + Control + S / Shift + Control + M (macOS) for keyboard-based solo and mute during testing.

What Multi-Decoder Mode is not

Multi-Decoder Mode is not:

• a direct Blauert-band decoder
• a distance renderer by itself
• automatically better than a single decoder
• a substitute for correct geometry, speaker verification, and routing discipline

Its strength lies in controlled comparison: you can separate loudspeaker groups and test how order, weighting, gain, and filtering affect the perceived result.

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):

This setup allows fine-tuned decoding for each layer independently, with separate gain compensation for the height speakers. The split can be useful because the horizontal ring and the height layer do not always benefit from identical decoding settings. The main ring often carries the most stable image, while the height layer may require more careful tuning to avoid sounding weak, blurry, or detached.

Further Resources

• 📖 ICST AmbiDecoder Wiki
• 📥 Download v3.2
• 📺 ICST Ambisonics Videos on YouTube