diff options
| -rw-r--r-- | docs/3D7.1.txt | 82 | ||||
| -rw-r--r-- | docs/ambisonics.txt | 119 | ||||
| -rw-r--r-- | presets/3D7.1.ambdec | 43 | ||||
| -rw-r--r-- | presets/hexagon.ambdec | 51 | ||||
| -rw-r--r-- | presets/presets.txt | 36 | ||||
| -rw-r--r-- | presets/rectangle.ambdec | 45 | ||||
| -rw-r--r-- | presets/square.ambdec | 45 |
7 files changed, 421 insertions, 0 deletions
diff --git a/docs/3D7.1.txt b/docs/3D7.1.txt new file mode 100644 index 00000000..1d40bec6 --- /dev/null +++ b/docs/3D7.1.txt @@ -0,0 +1,82 @@ +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. diff --git a/docs/ambisonics.txt b/docs/ambisonics.txt new file mode 100644 index 00000000..77ec8ef7 --- /dev/null +++ b/docs/ambisonics.txt @@ -0,0 +1,119 @@ +OpenAL Soft's renderer has advanced quite a bit since its start with panned +stereo output. Among these advancements is support for surround sound output, +using psychoacoustic modeling and more accurate plane wave reconstruction. The +concepts in use may not be immediately obvious to people just getting into 3D +audio, or people who only have more indirect experience through the use of 3D +audio APIs, so this document aims to introduce the ideas and purpose of +Ambisonics as used by OpenAL Soft. + + +What Is It? +=========== + +Originally developed in the 1970s by Michael Gerzon and a team others, +Ambisonics was created as a means of recording and playing back 3D sound. +Taking advantage of the way sound waves propogate, it is possible to record a +fully 3D soundfield using as few as 4 channels (or even just 3, if you don't +mind dropping down to 2 dimensions like many surround sound systems are). This +representation is called B-Format. It was designed to handle audio independent +of any specific speaker layout, so with a proper decoder the same recording can +be played back on a variety of speaker setups, from quadrophonic and hexagonal +to cubic and other periphonic (with height) layouts. + +Although it was developed over 30 years ago, various factors held ambisonics +back from really taking hold in the consumer market. However, given the solid +theories backing it, as well as the potential and practical benefits on offer, +it continued to be a topic of research over the years, with improvements being +made over the original design. One of the improvements made is the use of +Spherical Harmonics to increase the number of channels for greater spatial +definition. Where the original 4-channel design is termed as "First-Order +Ambisonics", or FOA, the increased channel count through the use of Spherical +Harmonics is termed as "Higher-Order Ambisonics", or HOA. The details of higher +order ambisonics are out of the scope of this document, but know that the added +channels are still independent of any speaker layout, and aim to further +improve the spatial detail for playback. + +Today, the processing power available on even low-end computers means real-time +Ambisonics processing is possible. Not only can decoders be implemented in +software, but so can encoders, synthesizing a soundfield using multiple panned +sources, thus taking advantage of what ambisonics offers in a virtual audio +environment. + + +How Does It Help? +================= + +Positional sound has come a long way from pan-pot stereo (aka pair-wise). +Although useful at the time, the issues became readily apparent when trying to +extend it for surround sound. Pan-pot doesn't work as well for depth (front- +back) or vertical panning, it has a rather small "sweet spot" (the area the +head needs to be in to perceive the sound in its intended direction), and it +misses key distance-related details of sound waves. + +Ambisonics takes a different approach. It uses all available speakers to help +localize a sound, and it also takes into account how the brain localizes low +frequency sounds compared to high frequency ones -- a so-called psychoacoustic +model. It may seem counter-intuitive (if a sound is coming from the front-left, +surely just play it on the front-left speaker?), but to properly model a sound +coming from where a speaker doesn't exist, more needs to be done to construct a +proper sound wave that's perceived to come from the intended direction. Doing +this creates a larger sweet spot, allowing the perceived sound direction to +remain correct over a larger area around the center of the speakers. + + +How Is It Used? +=============== + +As a 3D audio API, OpenAL is tasked with playing 3D sound as best it can with +the speaker setup the user has. Since the OpenAL API does not explicitly handle +the output channel configuration, it has a lot of leeway in how to deal with +the audio before it's played back for the user to hear. Consequently, OpenAL +Soft (or any other OpenAL implementation that wishes to) can render using +Ambisonics and decode the ambisonic mix for a high level of directional +accuracy over what simple pan-pot could provide. + +This is effectively what the high-quality mode option does, when given an +appropriate decoder configuation for the playback channel layout. 3D rendering +is done to an ambisonic buffer, which is later decoded for output utilizing the +benefits available to ambisonic processing. + +The basic, non-high-quality, renderer uses similar principles, however it skips +the frequency-dependent processing (so low frequency sounds are treated the +same as high frequency sounds) and does some creative manipulation of the +involved math to skip the intermediate ambisonic buffer, rendering more +directly to the output while still taking advantage of all the available +speakers to reconstruct the sound wave. This method trades away some playback +quality for less memory and processor usage. + +In addition to providing good support for surround sound playback, Ambisonics +also has benefits with stereo output. 2-channel UHJ is a stereo-compatible +format that encodes some surround sound information using a wide-band 90-degree +phase shift filter. It works by taking a B-Format signal, then deriving a +frontal stereo mix with some of the rear sounds filtered in with it. Although +the result is not as good as 3-channel (2D) B-Format, it has the distinct +advantage of only using 2 channels and being compatible with stereo output. +This means it will sound just fine when played as-is through a normal stereo +device, or it may optionally be fed to a properly configured surround sound +receiver which can extract the encoded information and restore some of the +original surround sound signal. + + +What Are Its Limitations? +========================= + +As good as Ambisonics is, it's not a magic bullet that can overcome all +problems. One of the bigger issues it has is dealing with irregular speaker +setups, such as 5.1 surround sound. The problem mainly lies in the imbalanced +speaker positioning -- there are three speakers within the front 60-degree area +(meaning only 30-degree gaps in between each of the three speakers), while only +two speakers cover the back 140-degree area, leaving 80-degree gaps on the +sides. It should be noted that this problem is inherent to the speaker layout +itself; there isn't much that can be done to get an optimal surround sound +response, with ambisonics or not. It will do the best it can, but there are +trade-offs between detail and accuracy. + +Another issue lies with HRTF. While it's certainly possible to play an +ambisonic mix using HRTF, doing so with a high degree of spatial detail +requires a fair amount of resources, in both memory and processing time. And +even with it, mixing sounds with HRTF directly will still be better for +positional accuracy. diff --git a/presets/3D7.1.ambdec b/presets/3D7.1.ambdec new file mode 100644 index 00000000..42b6a0bb --- /dev/null +++ b/presets/3D7.1.ambdec @@ -0,0 +1,43 @@ +# AmbDec configuration +# Written by Ambisonic Decoder Toolbox, version 8.0 + +/description 3D7_2h1v_allrad_5200_rE_max_1_band + +/version 3 + +/dec/chan_mask 1bf +/dec/freq_bands 1 +/dec/speakers 7 +/dec/coeff_scale fuma + +/opt/input_scale fuma +/opt/nfeff_comp output +/opt/delay_comp on +/opt/level_comp on +/opt/xover_freq 400.000000 +/opt/xover_ratio 0.000000 + +/speakers/{ +# id dist azim elev conn +#----------------------------------------------------------------------- +add_spkr LF 1.500000 51.000000 24.000000 +add_spkr RF 1.500000 -51.000000 24.000000 +add_spkr CE 1.500000 0.000000 0.000000 +add_spkr LB 1.500000 180.000000 55.000000 +add_spkr RB 1.500000 0.000000 -55.000000 +add_spkr LS 1.500000 129.000000 -24.000000 +add_spkr RS 1.500000 -129.000000 -24.000000 +/} + +/matrix/{ +order_gain 1.000000 0.774597 0.400000 0.000000 +add_row 0.325031 0.357638 0.206500 0.234037 0.202440 0.135692 0.116927 -0.098768 +add_row 0.325036 -0.357619 0.206537 0.234033 -0.202427 -0.135680 0.116934 -0.098768 +add_row 0.080073 -0.000010 -0.000296 0.155843 -0.000016 -0.000011 -0.000623 0.163306 +add_row 0.353556 0.000002 0.408453 -0.288377 -0.000004 -0.000003 -0.221039 0.077297 +add_row 0.325297 0.000008 -0.414018 0.232789 0.000004 0.000003 -0.232940 0.018311 +add_row 0.353558 0.352704 -0.203542 -0.290124 -0.191868 -0.134582 0.110616 -0.038294 +add_row 0.353556 -0.352691 -0.203576 -0.290115 0.191871 0.134585 0.110612 -0.038293 +/} + +/end diff --git a/presets/hexagon.ambdec b/presets/hexagon.ambdec new file mode 100644 index 00000000..d45f2732 --- /dev/null +++ b/presets/hexagon.ambdec @@ -0,0 +1,51 @@ +# AmbDec configuration +# Written by Ambisonic Decoder Toolbox, version 8.0 + +/description Hexagon_2h0p_pinv_match_rV_max_rE_2_band + +/version 3 + +/dec/chan_mask 11b +/dec/freq_bands 2 +/dec/speakers 6 +/dec/coeff_scale fuma + +/opt/input_scale fuma +/opt/nfeff_comp input +/opt/delay_comp on +/opt/level_comp on +/opt/xover_freq 400.000000 +/opt/xover_ratio 0.000000 + +/speakers/{ +# id dist azim elev conn +#----------------------------------------------------------------------- +add_spkr LF 1.000000 30.000000 0.000000 +add_spkr RF 1.000000 -30.000000 0.000000 +add_spkr RS 1.000000 -90.000000 0.000000 +add_spkr RB 1.000000 -150.000000 0.000000 +add_spkr LB 1.000000 150.000000 0.000000 +add_spkr LS 1.000000 90.000000 0.000000 +/} + +/lfmatrix/{ +order_gain 1.000000 1.000000 1.000000 0.000000 +add_row 0.235702 0.166667 0.288675 0.288675 0.166667 +add_row 0.235702 -0.166667 0.288675 -0.288675 0.166667 +add_row 0.235702 -0.333333 0.000000 -0.000000 -0.333333 +add_row 0.235702 -0.166667 -0.288675 0.288675 0.166667 +add_row 0.235702 0.166667 -0.288675 -0.288675 0.166667 +add_row 0.235702 0.333333 0.000000 -0.000000 -0.333333 +/} + +/hfmatrix/{ +order_gain 1.414214 1.224745 0.707107 0.000000 +add_row 0.235702 0.166667 0.288675 0.288675 0.166667 +add_row 0.235702 -0.166667 0.288675 -0.288675 0.166667 +add_row 0.235702 -0.333333 0.000000 -0.000000 -0.333333 +add_row 0.235702 -0.166667 -0.288675 0.288675 0.166667 +add_row 0.235702 0.166667 -0.288675 -0.288675 0.166667 +add_row 0.235702 0.333333 0.000000 -0.000000 -0.333333 +/} + +/end diff --git a/presets/presets.txt b/presets/presets.txt new file mode 100644 index 00000000..fcc8128f --- /dev/null +++ b/presets/presets.txt @@ -0,0 +1,36 @@ +Ambisonic decoder configuration presets are provided here for common surround +sound speaker layouts. The presets are prepared to work with OpenAL Soft's high +quality decoder. By default all of the speaker distances within a preset are +set to the same value, which results in no effect from distance compensation. +If this doesn't match your physical speaker setup, it may be worth copying the +preset and modifying the distance values to match (note that modifying the +azimuth and elevation values in the presets will not have any effect; the +specified angles do not change the decoder behavior). + +Details of the individual presets are as follows. + +square.ambdec +Specifies a basic square speaker setup for Quadrophonic output, with identical +width and depth. Front speakers are placed at +45 and -45 degrees, and back +speakers are placed at +135 and -135 degrees. + +rectangle.ambdec +Specifies a narrower speaker setup for Quadrophonic output, with a little less +width but a little more depth over a basic square setup. Front speakers are +placed at +30 and -30 degrees, providing a bit more compatibility for existing +stereo content, with back speakers at +150 and -150 degrees. + +hexagon.ambdec +Specifies a flat-front hexagonal speaker setup for 7.1 Surround output. The +front left and right speakers are placed at +30 and -30 degrees, the side +speakers are placed at +90 and -90 degrees, and the back speakers are placed at ++150 and -150 degrees. Although this is for 7.1 output, no front-center speaker +is defined for the decoder, meaning that speaker will be silent for 3D sound +(however it may still be used with AL_SOFT_direct_channels or ALC_EXT_DEDICATED +output). A "proper" 7.1 decoder may be provided in the future, but due to the +nature of the speaker configuration will have trade-offs. + +3D7.1.ambdec +Specifies a 3D7.1 speaker setup for 7.1 Surround output. Although it's for 7.1 +output, the speakers for such a configuration need to be placed in different +positions for proper results. Please see docs/3D7.1.txt for more information. diff --git a/presets/rectangle.ambdec b/presets/rectangle.ambdec new file mode 100644 index 00000000..caf72318 --- /dev/null +++ b/presets/rectangle.ambdec @@ -0,0 +1,45 @@ +# AmbDec configuration +# Written by Ambisonic Decoder Toolbox, version 8.0 + +/description Rectangle_1h0p_pinv_match_rV_max_rE_2_band + +/version 3 + +/dec/chan_mask b +/dec/freq_bands 2 +/dec/speakers 4 +/dec/coeff_scale fuma + +/opt/input_scale fuma +/opt/nfeff_comp input +/opt/delay_comp on +/opt/level_comp on +/opt/xover_freq 400.000000 +/opt/xover_ratio 0.000000 + +/speakers/{ +# id dist azim elev conn +#----------------------------------------------------------------------- +add_spkr LF 1.000000 30.000000 0.000000 +add_spkr RF 1.000000 -30.000000 0.000000 +add_spkr RB 1.000000 -150.000000 0.000000 +add_spkr LB 1.000000 150.000000 0.000000 +/} + +/lfmatrix/{ +order_gain 1.000000 1.000000 0.000000 0.000000 +add_row 0.353553 0.500000 0.288675 +add_row 0.353553 -0.500000 0.288675 +add_row 0.353553 -0.500000 -0.288675 +add_row 0.353553 0.500000 -0.288675 +/} + +/hfmatrix/{ +order_gain 1.414214 1.000000 0.000000 0.000000 +add_row 0.353553 0.500000 0.288675 +add_row 0.353553 -0.500000 0.288675 +add_row 0.353553 -0.500000 -0.288675 +add_row 0.353553 0.500000 -0.288675 +/} + +/end diff --git a/presets/square.ambdec b/presets/square.ambdec new file mode 100644 index 00000000..547ed367 --- /dev/null +++ b/presets/square.ambdec @@ -0,0 +1,45 @@ +# AmbDec configuration +# Written by Ambisonic Decoder Toolbox, version 8.0 + +/description Square_1h0p_pinv_match_rV_max_rE_2_band + +/version 3 + +/dec/chan_mask b +/dec/freq_bands 2 +/dec/speakers 4 +/dec/coeff_scale fuma + +/opt/input_scale fuma +/opt/nfeff_comp input +/opt/delay_comp on +/opt/level_comp on +/opt/xover_freq 400.000000 +/opt/xover_ratio 0.000000 + +/speakers/{ +# id dist azim elev conn +#----------------------------------------------------------------------- +add_spkr LF 1.000000 45.000000 0.000000 +add_spkr RF 1.000000 -45.000000 0.000000 +add_spkr RB 1.000000 -135.000000 0.000000 +add_spkr LB 1.000000 135.000000 0.000000 +/} + +/lfmatrix/{ +order_gain 1.000000 1.000000 0.000000 0.000000 +add_row 0.353553 0.353553 0.353553 +add_row 0.353553 -0.353553 0.353553 +add_row 0.353553 -0.353553 -0.353553 +add_row 0.353553 0.353553 -0.353553 +/} + +/hfmatrix/{ +order_gain 1.414214 1.000000 0.000000 0.000000 +add_row 0.353553 0.353553 0.353553 +add_row 0.353553 -0.353553 0.353553 +add_row 0.353553 -0.353553 -0.353553 +add_row 0.353553 0.353553 -0.353553 +/} + +/end |