Rather than stopping voices/sources when the device becomes disconnected, the
context can be set to leave them alone. As a consequence, their state will
remain as playing and they'll keep their last known sample offset indefinately.
For applications mindful of this behavior, it will allow resetting or reopening
the device to reconnect and automatically resume where it left off.
For the second-order decoder. Since the delays are adjusted to avoid most high
frequency phase cancelation, the energy-based scaling with the number of
channels used creates a significant HF increase. Using the RMS-based scaling
seems to create a more level response, though it's not perfect either. More
testing and measurements may be needed.
The inverted atomic flag replaces test_and_set+clear with test_and_clear+set,
essentially inverting the flag status. This makes more logical sense for
flagging dirty state, which is less confusing than flagging clean state. The
one caveat is ATOMIC_FLAG_INIT (or default construction in C++20) initializes
the state to true rather than false.
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 HOA signals, the number of responses used with slightly varying delays
causes noticeable attenuation in the higher frequencies because of destructive
phase interference. This is not a result of minimum phase alignment (attempts
to compensate for minimum phase had negligible results), nor does it affect
first-order signals (which only has 4 unique responses on each side).
This alternate alignment is only used when doing second-order rendering for
HRTF output, which is not the default with HRTF. It's likely not very ideal,
but it's necessary to prevent second-order rendering with HRTF from sounding
muffled.
