O1A Decoder - 9.1.6

Host Support

Host Type	Support
AAX	Yes
VST2	Yes

Audio

	Channels	Content
Input	4	O1A
Output	16	9.1.6 Surround

Controls

Method
LFE Crossover
LFE Gain

Description

This plugin takes a first order ambisonics (O1A) mix and decodes it to 9.1.6.

The AAX version of this specific plugin requires Pro Tools 2023.6 or later.

Channels

The channel ordering used is:

Channel	AAX	VST
1	Front Left	Front Left
2	Front Centre	Front Right
3	Front Right	Front Centre
4	Left Wide	LFE
5	Right Wide	Left Wide
6	Left Surround Side	Right Wide
7	Right Surround Side	Left Surround Side
8	Left Surround Rear	Right Surround Side
9	Right Surround Rear	Left Surround Rear
10	LFE	Right Surround Rear
11	Left Front Overhead	Left Front Overhead
12	Right Front Overhead	Right Front Overhead
13	Left Middle Overhead	Left Middle Overhead
14	Right Middle Overhead	Right Middle Overhead
15	Left Rear Overhead	Left Rear Overhead
16	Right Rear Overhead	Right Rear Overhead

Spatial Audio Compatibility Warning

Please note that the speaker angles assumed here have front left and right at +/-30 degrees, which match standard use in loudspeaker layouts. However, it appears that binaural Spatial Audio renderers commonly render front left and right bed channels at +/-45 degrees instead, which is close to the "wide" channels and leaves relatively large gaps at the front.

It might be tempting to encode 9.1.6 into a Spatial Audio stream as a 7.1 bed plus eight extra objects for the wide and raised channels, but this discrepancy means that final results are likely to be non-optimal when rendered on headphones rather than on loudspeakers.

This issue was one of the reasons we settled on the dome layout designs used in O3A Spatial Audio and O7A Spatial Audio, which use objects only and typically give better and more consistent results.

The plugin is available in the O1A Decoding plugin library.

Controls

Control: Method

Three methods are supported, "Basic", "Reconstruction" and "Tinted Reconstruction". Generally, "Basic" is recommended except where the speaker rig to be used for playback is known and has been set up accurately.

Method	Description
Basic	This method produces a resilient decoding which should play well on a range of speaker systems including large venues.
Reconstruction	This method controls the soundfield at the centre of the listening space to produce a clearer spatial image. It relies on the speaker layout being set up accurately.
Tinted Reconstruction	This variant of the Reconstruction method performs HRTF-based tinting on the audio stream to strengthen the spatial image. Again, it relies on the speaker layout being set up accurately.

Control: LFE Crossover

This determines if any audio is sent to the LFE channel. It may be set to "Off" and this is recommended. If enabled, audio is extracted from the main mix into the LFE channel using the indicated crossover frequency (between 1 and 200Hz).

Control: LFE Gain

If the LFE gain is active, this gain is applied to it. Some export formats may need this set to -10dB to take into account a +10dB gain applied during playback.

O1A Decoding