Monitor Mission - Downmix Rules

As of the Firmware release 2.0 for Anubis and Neumann MT 48, we provide the user a flexible way to customize the Downmix Rules in the Monitor Mission. 
This requires that users follow the special procedure described below.

• Overview
• Channel Naming Convention
• How Downmixing Works
• JSON File Structure
• Editing Guidelines
• Import Validation and Error Messages
• Best Practices When Customizing
• Providing the JSON via Monitor Mission (Anubis / MT48)
• Summary

1. Overview

The Downmix JSON file defines how audio channels should be remapped when the destination monitor does not contain the same set of channels as the source audio format.

Here is the default JSON file. We suggest to use it as a modification base.

2. Channel Naming Convention

Each channel type is represented by a short identifier. These identifiers correspond to internal audio channel enums.

These names must be used exactly as listed when editing the JSON file.

3. How Downmixing Works - Core Principles

When a source channel is played through a monitor profile:

The system first checks whether the destination monitor contains the same channel.
If the channel is missing in the monitor, the system searches the channel’s downmix substitution list in the JSON.
Substitutions are tried in order until a channel present in the monitor is found.
Each substitution applies a gain in dB, for example:

 {"L": -3, "R": -3}

→ send the source to Left and Right with –3 dB gain.

Example:
If a source contains Center (C), but the monitor only has L and R, this rule applies:

"C": [
  {"C": 0},
  {"L": -3, "R": -3}, ← used when C is not available
  …
]

Thus, C is downmixed to L and R at –3 dB.

4. JSON File Structure

The file contains three main sections:

{
  "Downmix": { ... },
  "Downmix_Surround_To_Side": { ... },
  "Downmix_Surround_To_SideAndRear": { ... }
}

4.1 Downmix

Defines the default downmix rules for every channel type.
Each entry must be an array (even if containing only one rule).
Example:

"L": [
  {"L": 0},
  {"C": -6.02},
  {"Lrs": -3}
]

4.2 Downmix_Surround_To_Side

Used when the settings > Monitor Levels > 5.1 to 7.1 Monitoring is set to Ls/Rs to Lss/Rss
Example:

"Downmix_Surround_To_Side": {
  "Lrs": [...],
  "Rrs": [...]
}

4.3 Downmix_Surround_To_SideAndRear

Used when the settings > Monitor Levels > 5.1 to 7.1 Monitoring is set to Ls/Rs to Lss-Lrs/Rss-Rrs
Example:

"Downmix_Surround_To_SideAndRear": {
  "Lrs": [...],
  "Rrs": [...]
}

5. Editing Guidelines

When modifying the JSON file:

Keep all channel keys present inside "Downmix" (even if empty for the "-" entry).
Each channel definition must be an array.
Each array element must be a mapping:

{"<destination_channel>": <gain_in_dB>}

You may include multiple destination channels in one rule.
The system uses the first valid matching rule found in the array.

6. Import Validation and Error Messages

When you import a JSON file, the system performs the following checks:

6.1 Required top-level objects

• "Downmix" must exist.

• "Downmix_Surround_To_Side" must exist.

• "Downmix_Surround_To_SideAndRear" must exist.

Error example:
'Downmix' object missing. Not a valid Downmix JSON
 

6.2 Each channel must be present

For all known channel types, the "Downmix" object must contain an entry:

Error example:
Channel Lrs object missing. Not a valid Downmix JSON
 

6.3 Each channel entry must be an array

Error example:
Channel C is not array. Not a valid Downmix JSON
 

6.4 Arrays cannot be empty (except for "-" entry)

Error example:
Channel R array cannot be empty. Not a valid Downmix JSON
 

6.5 Surround Downmix sections must contain Lrs and Rrs

For both:

• "Downmix_Surround_To_Side"

• "Downmix_Surround_To_SideAndRear"

Error example:
Channel Lrs object missing in Downmix_Surround_To_Side. Not a valid Downmix JSON
 

6.6 File writing errors

If saving the imported file fails:

Error example:
Failed to create file CustomDownmix.json ... JSON import fails
 

6.7 Invalid files are automatically deleted

When any validation error occurs:

• The temporary imported file is removed.

• An error message is logged.

• The system keeps the previous valid JSON.

7. Best Practices When Customizing

• Always validate your JSON with a JSON validator before importing.

• Avoid removing channels: keep entries even if you do not use them.

• Maintain numerical values as dB gains (float or integer).

• Avoid duplication: if two rules are identical, keep only one.

• Keep the ordering logical: most likely substitutions first.

8. Providing the JSON via Monitor Mission (Anubis / MT48)

The configuration file can be uploaded using the Monitor Mission web interface

A warning will appear if your file is invalid, with the exact validation error corresponding to the rules above.

9. Summary

This JSON file allows complete customization of audio downmixing behavior in Anubis / MT48. The system uses strict validation to ensure the data is complete and correctly formatted. By following the structure and rules described above, you can safely define custom downmix behaviors for any monitoring configuration.