Despite the claim that it was an 11th order filter, the transition width was
generated by specifying 12th order. A 12th order filter would need 14 sample
points rather than the 12 it had.
Rather than storing individual pointers to filter, scale delta, phase delta,
and scale phase delta entries, per phase index, the new table layout makes it
trivial to access the per-phase filter and delta entries given the base offset
and coefficient count.
The old layout separated filters, scale deltas, phase deltas, and scale phase
deltas into separate segments that each contained a numbers of scale and phase
entries, Since processing a sample needed a filter and one of each delta entry
relating to a particular scale and phase, the memory needed would be spread
across the whole table. And since subsequent samples would use a different
phase, it would jump around the table a whole lot as well.
The new layout packs the data in a way more consistent with its use. The
filters, scale deltas, phase deltas, and scale phase deltas are interleaved,
such that for a particular scale and phase, the filter and delta entries used
are contiguous. And the phase entries for a particular scale are kept together,
so the ~500 to ~1000 samples processed per source update stay within the same
3KB to 6KB area of the 70+KB table, which is much more cache friendly.
Currently makehrtf only handles 24-bit output, not dual-ear, and only when
given the --experimental switch. Files produced this way will not be guaranteed
future compatibility. When the mhr format is also updated with multi-distance
measurements, the experimental switch can go away.
This improves a stereo (front-left + front-right) sound "image" by generating a
front-center channel signal. Done correctly, it helps reduce the comb effects
and phase errors associated with using only two speakers to simulate center
sounds.
Note that it shouldn't be used if the front-center channel is already included
in the positional audio mix (the dialog effect is okay). In general, it may
actually be better to exclude the front-center channel from the positional
audio mix and use this to generate front-center output.
Not all speaker kits have a front-center speaker capable of outputing full-
range content. It's best to err on the side of caution and not include front-
center for normal positional sound by default, leaving it instead for the
dedicated dialog effect.
On some speaker setups, the front-center speaker is not designed for full-range
content and should be used exclusively for dialog. Consequently it should not
be used for positional sounds, only the dedicated dialog effect.
This is rather ugly, but it's necessary to get a proper export configuration.
The issue was that the main OpenAL target library name is set to soft_oal when
the router is being built, which is incorrect for the exported config library.
Exporting the router would have the incorrect name of OpenAL::Router.
So this change has the router use the OpenAL target name when it's built, which
is good since it will have the standard OpenAL lib name for apps to link to and
get the OpenAL::OpenAL export name. The main library's target name is changed
in this case to avoid conflicts.
