reaper_ambix – read/write .ambix files - lossless and lossy Ambisonic compression, loudness normalization, ...

reaper_ambix is a free extension for the REAPER DAW that reads and writes .ambix files – the Ambisonics exchange format (C. Nachbar, F. Zotter, E. Deleflie, A. Sontacchi, ambiX – A Suggested Ambisonics Format, Ambisonics Symposium, Lexington, 2011) that goes with the ambiX plug-ins – and adds a few tools for working with Ambisonic sessions. I started it in 2014 and recently gave it a major update.

Source properties of an .ambix file in REAPER

.ambix as render format and media type

Files can be written as uncompressed CAF, lossless WavPack, or lossy WavPack in hybrid mode at 6, 4 or 3 bits per sample. The noise floor of the lossy mode follows each channel’s level, so the quiet higher-order channels stay quiet and the result survives decoding and rotation.

The item’s source properties show the format and the tags of WavPack files, and markers and regions stored in a file appear as cues.

Render settings

WavPack lossy settings

Compression

An example: a 12 min 27 s Spacemic recording at 48 kHz / 24 bit, encoded to 5th order.

	Size	vs. .wav
Raw Spacemic recording, 84 microphone channels	9.02 GB
5th order, 36 channels, .wav	5.17 GB	100 %
.ambix, WavPack lossless	2.07 GB	40 %
.ambix, WavPack lossy (6.2 bits/sample)	998 MB	19 %

The lossless file is bit-identical to the .wav at 40 % of its size. The lossy file is a fifth of the size.

Actions

Normalize selected items to a target loudness (LUFS), or just measure it. BS.1770-4; Ambisonic items are measured on the W channel (following N. Peters, N. Epain, Loudness Perception of Scene-Based Audio across Loudspeaker Configurations and HOA Orders, AES Convention Paper 10658, 154th AES Convention, Espoo, 2023), surround layouts up to 9.1.4 per BS.1770-5.
Set channel count of selected tracks and their sends – switch a whole session between Ambisonic orders in one step.
Convert items to .ambix files, optionally adding them as a new take.
Convert FuMa to ambiX (ACN/SN3D), up to 3rd order.

Loudness normalization turned out to be very helpful for judging the 3D Audio Competition: with all submissions at the same loudness, they can be compared on their merits rather than their level.

The ambiX actions in REAPER's action list

Normalize progress dialog: 36 channels, ambisonic, measuring W only — Normalizing: Ambisonic items are measured on W

Normalized items with their gain offsets and the console log

REAPER Live

REAPER Live comes with it: a touch mixer and transport for a phone or tablet, served by REAPER’s own web server – handy for recording sessions and concerts away from the computer.

Installation

In REAPER choose Extensions → ReaPack → Import repositories… and paste

https://github.com/kronihias/reaper_ambix/raw/master/index.xml

then install reaper_ambix and/or REAPER Live from Extensions → ReaPack → Browse packages and restart REAPER. Installers for macOS, Windows (x64 and ARM) and Linux are on the releases page.

Source code, documentation and bug reports: github.com/kronihias/reaper_ambix (LGPL). Built on libambix by IOhannes m zmölnig and WavPack by David Bryant.