Auro-3D

What Auro-3D is

Auro-3D is an immersive audio format built on layers of speakers rather than a pool of audio objects. It was introduced by Wilfried Van Baelen, then CEO of Galaxy Studios and Auro Technologies, at the AES Convention in 2006 with the Auro 9.1 and Auro 10.1 speaker layouts. Auro's own setup guidelines describe a bottom surround layer (5.1 or 7.1), a height layer above it, and in larger rooms a third layer with a single top speaker. Auro calls the format a hybrid: channel-based in its home layouts, with object technology reserved for the cinema system AuroMax, which combines up to 64 object channels with up to Auro 13.1 beds.

How Auro-3D works: layers and the Auro-Codec

Auro 9.1 is a 5.1 surround layer plus four height speakers (front left and right, and left and right surround height). That is nine full-range channels plus an LFE, which is the same speaker count as a 5.1.4 Atmos layout. Auro 10.1 adds a Top speaker at 90 degrees directly above the seat, nicknamed Voice of God. Auro 11.1 adds a Height Center for six front channels across two vertical planes, and Auro 13.1 builds on a 7.1 surround layer with four heights, the height center and the top. Auro 11.1 (7+4) is a two-layer variant that sits on a 7.1 base.

Placement is specific. Research at Galaxy Studios found an ideal height-layer angle between 25 and 35 degrees, and the guidelines say the height speakers should be elevated to 30 degrees and tilted so their acoustic center aims at the listener's head. If the surround layer must be raised, it should not exceed 10 degrees of elevation, and a minimum of 25 degrees must separate the surround and height layers, which pushes the height layer to at least 35 degrees. Auro says the Voice of God channel is not crucial to the experience and is limited to fly-overs and special effects. Compare with height speaker elevation angle.

The Auro-Codec carries the extra channels inside ordinary PCM. Per Auro's Engine white paper, it stays in the PCM domain, uses no perceptual coding, and can mix and unmix up to three channels of PCM audio from a single encoded carrier channel. One carrier can hold an Auro mix, a surround version and a stereo version, and the surround carrier plays on any digital audio system even without an Auro decoder. Auro-Matic, the upmixer, keeps the original channels of the source intact and places the recording in a three-dimensional environment, while Auro-Scene virtualizes the format for other speaker layouts.

Auro-3D vs Dolby Atmos and DTS:X

The structural difference is authoring. Dolby Atmos masters hold up to 128 channels, a 7.1.2 bed plus 118 objects, and the renderer maps them to your speakers (see audio objects vs bed channels). Auro-3D home content is authored for a fixed family of layouts from 9.1 to 13.1 and scaled down or up by the Auro-3D Engine. The upside is predictable height placement at a known angle.

Hands-on testing shows how the upmixers differ. High-Def Digest compared the Dolby Surround Upmixer, DTS Neural:X and Auro-Matic on a Denon AVR-X8500H and found that Neural:X and Auro-3D were limited to 7.1.4 processing and ignored the top-middle speakers, while the Dolby upmixer used all three height pairs. The reviewer heard Neural:X push helicopter effects to the heights loudly, Auro land in between, and judged that Auro appears to copy the ground channels into the heights with a little reverb added. That is one reviewer on one receiver in 2018, so treat it as a description of character rather than a standard. See Dolby Surround upmixer and DTS Neural:X.

Which gear and content support Auro-3D

The Denon AVR-X3800H lists Auro 3D alongside Dolby Atmos, DTS:X and IMAX Enhanced, with 9.4 channels at 105 W. The Denon AVR-X8500H shipped with the Auro-3D upmixer included, where it had previously been a $199 add-on. Auro states that the Auro-3D Engine (Codec, Matic and Scene) is included in supporting AV receivers and processors, that native content plays from Blu-ray discs or via streaming through the Auro-Codec, and that soundbars are supported through virtualization.

Auro recommends Auro 9.1 or 11.1 (7+4) for small and medium living-room systems and Auro 10.1, 11.1 or 13.1 for larger home cinemas. Its guidelines define a small room as a single row of up to 4 seats with a screen up to 105 inches, and a large room as 2 or 3 rows with screens over 120 inches. Auro 11.1, Auro 13.1 and the Auro-Codec launched at the Spatial Audio Convention in Tokyo in October 2010, Barco partnered with Auro in 2011 for cinema hardware, and Red Tails was announced as the first major film in Auro 11.1. Check layout options with the speaker layout tool.

Common confusions

Auro 9.1 and Atmos 5.1.4 are not the same thing despite the equal speaker count. Auro counts all full-range channels in the first number and fixes the height speakers at about 30 degrees; Atmos notation separates floor, LFE and overhead counts. The two formats also differ in how content reaches them: Atmos mixes are rendered from objects, while Auro mixes are decoded from a PCM carrier. Read channel configuration notation to translate between them.

Auro-3D support is not universal. High-Def Digest notes the upmixer was a $199 add-on before Denon bundled it, so a receiver that lists Atmos and DTS:X may not include Auro. Check the spec sheet before assuming support, and see the Atmos upgrade guide for how heights fit into a 5.1 system.