The extended precision of the encoder's 0.6512*X term was guesswork, with no
real basis for it. Switch back to the original value until something better
actually comes up. Also updates the decoder to account for the change in the
encoder.
Classic B-Format uses scaling factors W=1, X=sqrt(2), Y=sqrt(2), and Z=sqrt(2),
which is +3dB louder than FuMa. The base factors are designed assuming classic
scaling, so encoding a 0dBFS FuMa signal without accounting for this would
result in the UHJ signal peaking at about -3dBFS. Similarly, decoding UHJ to
FuMa B-Format would be +3dB louder than intended.
So encoding needs to implicitly boost the signal by +3dB, and decoding needs to
attenuate by -3dB.
For 2-channel UHJ, two decoding equations are provided in the original paper.
The alternative one is most often referenced for 2-channel UHJ decoding, but
the original/general one can also be used by assuming T is fully attenuated
(which the format allows for, as T can be variably attenuated by a factor
between 0 and 1 to deal with an imperfect transmission medium).
Neither method can be perfect for 2-channel UHJ, it's irrevocably lossy to the
original source, but my subjective testing indicates the general equation
produces less audibly errant results.
There are no known file formats intended to support 3- and 4-channel UHJ, but
it is possible to store them in various audio files when a player/decoder is
aware of what it's dealing with. So there's no reason not to have it as an
option.
Currently only supports 2-channel UHJ, and the produced .amb files shouldn't be
played as normal B-Format (decoded 2-channel UHJ needs to use different shelf
filters).
