There were phase issues caused by applying HRTF directly to the B-Format
channels, since the HRIR delays were all averaged which removed the inter-aural
time-delay, which in turn removed significant spatial information.
This mixes to a 4-channel first-order ambisonics buffer. With ACN ordering and
N3D scaling, this makes it easy to remain compatible with effects that only
care about mono input since channel 0 is an unattenuated mono signal.
This helps the stability of transforms to local space for sources that are at
or near the listener. With a single-precision matrix, even FLT_EPSILON might
not be enough to detect matching positions.
This is essentially a 12-point sinc resampler, unless it's resampling to a rate
higher than the output, at which point it will vary between 12 and 24 points
and do anti-aliasing to avoid/reduce frequencies going over nyquist.
Code provided by Christopher Fitzgerald.
The extension's not going anywhere, and it can't do anything fluidsynth can't.
The code maintenance and bloat is not worth keeping around, and ideally the AL
API would be able to facilitate MIDI-like behavior anyway (envelopes, start-at-
time, etc).
Note that this is the multiple above the device sample rate, rather than the
source property limit. It could theoretically be increased to 511 by testing
against UINT_MAX instead of INT_MAX, since the increment and positions are
using unsigned integers. I'm just being paranoid about overflows.
Note that it still uses FuMa scalings internally. Coefficients loaded from
config files specify if they're FuMa (in both ordering and scaling) or N3D,
and will get reordered or rescaled as needed.
This reverts commit 7ffb9b3056ab280d5d9408fd023f3cfb370ed103.
It was behaving as appropriate before (orienting left did pan it left for the
listener), I was apparently just misinterpreting the matrix.
The rotation erroneously specified the orientation of the source relative to
the sound field, whereas it should be the orientation of the sound field *and*
source relative to the listener. So now when the source is oriented left, the
front of the sound field is to the left of the listener.
For sources with a non-0 radius:
When distance <= radius, factor = distance/radius*0.5
When distance > radius, factor = 1 - asinf(radius/distance)/PI
Also, avoid using Position after calculating the localized direction and
distance.
This method is intended to help development by easily testing the quality of
the B-Format encode and B-Format-to-HRTF decode. When used with HRTF, all
sources are renderer using the virtual B-Format output, rather than just
B-Format sources.
Despite the CPU cost savings (only four channels need to be filtered with HRTF,
while sources all render normally), the spatial acuity offered by the B-Format
output is pretty poor since it's only first-order ambisonics, so "full" HRTF
rendering is definitely preferred.
It's /possible/ for some systems to be edge cases that prefer the CPU cost
savings provided by basic over the sharper localization provided by full, and
you do still get 3D positional cues, but this is unlikely to be an actual use-
case in practice.
This adds the ability to directly decode B-Format with HRTF, though only first-
order (WXYZ) for now. Second- and third-order would be easilly doable, however
we'd need to be able to up-mix first-order content (from the BFORMAT2D and
BFORMAT3D buffer formats) since it would be inappropriate to decode lower-order
content with a higher-order decoder.
