With virtualization disabled, channels are mapped directly from input to output
and any input channel that is missing an output is dropped. Any virtualization
effects (such as HRTF filters) for positional cues are also skipped.
The idea is to allow applications a way to play pre-filtered audio that channel
vitualization effects could interfere with.
Applications that are not built around OpenAL's orientation system need to
convert their given vectors to it. Depending on how this is done, it can lead
to proper stereo (left-right) panning with improper surround sound (front-back)
panning, which thusly sounds correct with stereo output and incorrect with 4+
channel output.
This option is intended to help fix playback of such applications on surround
sound systems, without having to resort to forcing stereo output.
The data is based on the KEMAR HRTF data provided by MIT, which can be found at
<http://sound.media.mit.edu/resources/KEMAR.html>. The compact measurements
were used. See hrtf_tables.inc for more information.
The filter is only available for stereo output, using a 44100hz playback rate.
Note also that it currently only applies to mono sounds, and the cf_level and
head_dampen config options are ignored while it is active.
All previous versions of the library treated the source cone angles as half
angles, which is contrary to the spec. Setting the __ALSOFT_HALF_ANGLE_CONES
environment variable to "true" or "1" restores the buggy behavior for
compatibility with applications that expect it.
This is not a config file option because new apps should not be made to depend
on the old behavior.
The spec intends the property values to be the full angle encompassed by the
cones, but the calculation interprets them as the angle from the center
point.
Mono sources and effects already output according to the available output
device channels. Multiplying the device matrix with the source matrix results
in a matrix that has the same effect as applying the source matrix followed by
the device matrix, so all the channel remixing can be done in one place.
