a
alareis
Second world: two zones, both use first order AmbiX-style ambisonic clip. ONSP-spatialised one requires a specific setup which involves 2D mixing and decoding via ONSP middleware, while SA doesn't natively support AmbiX-style ambisonics, but can passably parse them under binaural HRTF mix. While not a correct way to do it, in a pinch this method can be used just as well.
Unlike ONSP, SA handles spatial mixing just fine, but it doesn't handle 2D sources. Sources not upgraded to SA middleware are read as full track mixdowns instead of being processed as ambisonic clips, meaning you lose channel 3 and 4, along with directionality. Non-spatialised sources are also read as a basic mixdown.
Technically speaking, losing direct first order ambisonics is not a significant issue
only
if we can gain access to post-process effects, as they are mixed down to ambisonic streams themselves. Effectively, having middleware that's capable of producing ambisonic streams is more straightforward than mixing phase dips yourself; 3D environment acting as a form of a DAW is much more convenient.
However, this is an issue when it comes to backwards compatibility. As it stands, there doesn't seem to be a valid way to convert ONSP ambisonics to SA spatialisation, not out of the box.
As such, here are some examples of what breaks:
  1. wrld_08f14312-1f6b-4284-ba18-e6443c2a6a8f: environment track is no longer spatialised properly, always appearing static (though this is true for current mainline just as well)
  2. wrld_aa458f70-972b-494b-9eaf-6f6b1483ca9b: ONSP ambix clip is broken the same way
  3. wrld_c716477a-de43-4fe1-8a87-9177cc05345e: ambisonics are preserved but appear rotated about 45° CW with significantly reduced mids (~1500-7000 Hz); no idea what ambisonics formats are used there