O3A Decoder - 3D7.1

Host Support

Host Type	Support
AAX	Yes, output mapped to 7.1
VST2	Yes

Audio

	Channels	Content
Input	16	O3A
Output	8	3D7.1 Surround (mapped to 7.1 for AAX)

Controls

Method
LFE Crossover
LFE Gain

Description

This plugin takes a third order ambisonics (O3A) mix and decodes it as a 3D7.1 surround mix.

3D7.1 is a modified version of the 7.1 speaker layout invented by Simon N. Goodwin. It is based on the equipment used for 7.1 but places the speakers in different locations, some being raised or lowered.

If you intend to use this decoder then you should move your speakers to these new locations. Alternatively there is a normal O3A decoder for 7.1.

Channel Ordering for AAX

For AAX, the channel ordering and assumed speaker locations for the 3D7.1 surround mix are as follow.

Channel	7.1 Speaker Position	3D7.1 Speaker Position	Azimuth	Elevation	Used in 5.1
1	Front Left	Front Left High	+51	+24	Yes
2	Front Centre	Front Centre	0	0	Yes
3	Front Right	Front Right High	-51	+24	Yes
4	Left Surround Side	Rear Left Low	+129	-24	Yes
5	Right Surround Side	Rear Right Low	-129	-24	Yes
6	Left Surround Rear	Rear Centre High	+180	+55	No
7	Right Surround Rear	Front Centre Low	0	-55	No
8	LFE	LFE	-	-	Yes

VST

For VST, the channel ordering and assumed speaker locations for the 3D7.1 surround mix are as follow.

Channel	7.1 Speaker Position	3D7.1 Speaker Position	Azimuth	Elevation	Used in 5.1
1	Front Left	Front Left High	+51	+24	Yes
2	Front Right	Front Right High	-51	+24	Yes
3	Front Centre	Front Centre	0	0	Yes
4	LFE	LFE	-	-	Yes
5	Rear Left	Rear Centre High	+180	+55	No
6	Rear Right	Front Centre Low	0	-55	No
7	Side Left	Rear Left Low	+129	-24	Yes
8	Side Right	Rear Right Low	-129	-24	Yes

In the tables above, azimuth is measured anticlockwise (left) from the front and elevation upwards from the horizontal.

The plugin is available in the O3A 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.

O3A Decoding