EDIT: You can download a JS effect (for Reaper) that does the conversion from ambiX to TBE and another that goes from TBE to 2nd order, 2D, Furse-Malham format here (I’ve included my remapping JS effect too, so you can also go from Furse-Malham to TBE format by converting to that first 🙂 :
Angelo Farina has published an excellent article detailing how the 9, 2nd order Ambisonic components map to the 8 channels of the Facebook360 TBE format (they decided to pander to the 8-channel limit of pro-tools 🙁 ). All the details can be found at Angelo’s website:
The important bit, for my own notes, is (with added Furse-Malham mapping):
TBE(1) = 0.486968 * Ambix(1) (FuMa W) TBE(2) = -0.486968 * Ambix(2) (FuMa Y) TBE(3) = 0.486968 * Ambix(4) (FuMa X) TBE(4) = 0.344747 * Ambix(3) + 0.445656 * Ambix(7) (FuMa Z+R) TBE(5) = -0.630957 * Ambix(9) (FuMa U) TBE(6) = -0.630957 * Ambix(5) (FuMa V) TBE(7) = -0.630957 * Ambix(6) (FuMa T) TBE(8) = 0.630957 * Ambix(8) (FuMa S)
And, to go from TBE to 2nd order, 2D, Furse-Malham format (as mentioned by Ed, in the comments below):
W = 1.446968601 * TBE(1) X = 2.047502048 * TBE(3) Y = -2.047502048 * TBE(2) U = -1.839587932 * TBE(5) V = -1.839587932 * TBE(6)
TBE is Facebook360 Two Big Ears format
ambiX is the ambiX format used by YouTube Spatial Media (ACN channel order and SN3D normalisation)
FuMa is the Furse-Malham channel ordering and normalisation scheme.
See https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats for further details on channel ordering and normalisation schemes.
A polar plot of TBE Channel 4 (the combination of the Z and R channels in FuMa speak) can be seen above (click for higher res image).