Overview
========

3D7.1 is a custom speaker layout designed by Simon Goodwin at Codemasters[1].
Typical surround sound setups, like quad, 5.1, 6.1, and 7.1, only produce audio
on a 2D horizontal plane with no verticality, which means the envelopment of
"surround" sound is limited to left, right, front, and back panning. Sounds
that should come from above or below will still only play in 2D since there is
no height difference in the speaker array.

To work around this, 3D7.1 was designed so that some speakers are placed higher
than the listener while others are lower, in a particular configuration that
tries to provide balanced output and maintain some compatibility with existing
audio content and software. Software that recognizes this setup, or can be
configured for it, can then take advantage of the height difference and
increase the perception of verticality for true 3D audio. The result is that
sounds can be perceived as coming from left, right, front, and back, as well as
up and down.

[1] http://www.codemasters.com/research/3D_sound_for_3D_games.pdf


Hardware Setup
==============

Setting up 3D7.1 requires an audio device capable of raw 8-channel or 7.1
output, along with a 7.1 speaker kit. The speakers should be hooked up to the
device in the usual way, with front-left and front-right output going to the
front-left and front-right speakers, etc. The placement of the speakers should
be set up according to the table below. Azimuth is the horizontal angle in
degrees, with 0 directly in front and positive values go /left/, and elevation
is the vertical angle in degrees, with 0 at head level and positive values go
/up/.

------------------------------------------------------------
- Speaker label | Azimuth | Elevation |      New label     -
------------------------------------------------------------
- Front left    |    51   |     24    |   Upper front left -
- Front right   |   -51   |     24    |  Upper front right -
- Front center  |     0   |      0    |       Front center -
- Subwoofer/LFE |   N/A   |    N/A    |      Subwoofer/LFE -
- Side left     |   129   |    -24    |    Lower back left -
- Side right    |  -129   |    -24    |   Lower back right -
- Back left     |   180   |     55    |  Upper back center -
- Back right    |     0   |    -55    | Lower front center -
------------------------------------------------------------

Note that this speaker layout *IS NOT* compatible with standard 7.1 content.
Audio that should be played from the back will come out at the wrong location
since the back speakers are placed in the lower front and upper back positions.
However, this speaker layout *IS* more or less compatible with standard 5.1
content. Though slightly tilted, to a listener sitting a bit further back from
the center, the front and side speakers will be close enough to their intended
locations that the output won't be too off.


Software Setup
==============

To enable 3D7.1 on OpenAL Soft, first make sure the audio device is configured
for 7.1 output. Then in the alsoft-config utility, under the Renderer tab,
select the 3D7.1.ambdec preset for the 7.1 Surround decoder configuration. And
that's it. Any applications using OpenAL Soft can take advantage of fully 3D
audio, and multi-channel sounds will be properly remixed for the speaker
layout.

Playback can be improved by (copying and) modifying the 3D7.1.ambdec preset,
changing the specified speaker distances to match the the real distance (in
meters) from the center of the speaker array, then enable High Quality Mode in
alsoft-config. That will improve the quality when the speakers are not all
equidistant.

Note that care must be taken that the audio device is not treated as a "true"
7.1 device by non-3D7.1-capable applications. In particular, the audio server
should not try to upmix stereo and 5.1 content to "fill out" the back speakers,
and non-3D7.1 apps should be set to either stereo or 5.1 output.

As such, if your system is capable of it, it may be useful to define a virtual
5.1 device that maps the front, side, and LFE channels to the main device for
output and disables upmixing, then use that virtual 5.1 device for apps that do
normal stereo or surround sound output, and use the main device for apps that
understand 3D7.1 output.