Since commit c837484015, the backend's lock is no longer implicitly held when
calling capture functions. A separate mutex is used to ensure serial access,
and its up to the backend to protect against races and reentrancy with the
audio API.
It's hard to tell which is ultimately better, although this way does make the
FOA output somewhat louder which will help when it's combined with direct HRTF
rendering.
Use an empty source file to build a stub object file, instead of /dev/null. Use
_mh_dylib_header to retrieve the data on 10.7+, instead of _mh_execute_header.
And shorten the names to fit in the 16-character limit.
Thanks to Anna Cheremnykh for the fixes!
The original pseudo-inverse method that generated the LF matrix expects the
high frequencies to be scaled up by ~2.645751 over the low frequencies (or
sqrt(7), ~8.45dB). However, the AllRAD method used to generate the HF matrix
produced a matrix that was only scaled up by 1.46551981258 (based on the
average of the W coefficients).
Previously, the LF matrix was scaled down by sqrt(7), as the difference
specified in the pseudo-inverse results. This failed to account for the
increase already present in the HF matrix, so now the LF matrix is scaled down
by the remaining difference between the expected scaling and the scaling
already present in the HF matrix (sqrt(7) / 1.46551981258 = 1.80533302205, or
roughly 5.13dB, where the reciprocal is 0.553914423 for -5.13 dB).
It still fades between HRIRs when it changes, but now it selects the nearest
one instead of blending the nearest four. Due to the minimum-phase nature of
the HRIRs, interpolating between delays lead to some oddities which are
exasperated by the fading (and the fading is needed to avoid clicks and pops,
and smooth out changes).
Technically it uses A-Format processing from the B-Format input and output. But
this attempts to provide better spatial definition to the reverberation so that
it can be used in a more generic fashion, allowing it to be decoded as any
other B-Format signal to whatever output is needed, and also allowing for a bit
of height information when the output is capable of such.
There may still be some kinks to work out, such as properly decorrelating the
early reflection taps and tweaking the late reverb density. But it seems to be
a good enough start.
This uses an AllRAD-derived decoder matrix for the high frequencies, which
seems to improve positioning response. It also switches back to dual-band.
The low frequencies appear to be unexpectedly quiet by comparison, but it's not
that bad and can be tweaked later.
Designed for apps that either don't change the listener's AL_GAIN, or don't
allow the listener's AL_GAIN to go above 1. This allows the volume to still be
increased further than such apps may allow, if users find it too quiet.
Be aware that increasing this can easily cause clipping. The gain limit
reported by AL_GAIN_LIMIT_SOFT is also affected by this.
