This is needed for HeSuVi no-echo impulses, which are only one channel
per input channel, and mapping uses symmetrical mirroring of the input
set to create the surround effect, since there's no side-to-side delay
in these impulses.
This new virtualizer uses the Accelerate framework to process samples.
I've bundled a HeSuVi impulse for now, and will add an option to select
an impulse in the future. It will validate the selection before sending
it to the actual filter, which outright fails if it receives invalid
input. Impulses will be supported in any arbitrary format that Cog
supports, but let's not go too hog wild, it requires HeSuVi 14 channel
presets.
