Details on Facebook 360 Ambisonics Mapping from Angelo Farina

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 🙂 :

WigWare AmbiX, FuMa and TBE Tools

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:

http://pcfarina.eng.unipr.it/TBE-conversion.htm 

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).

 

5 Replies to “Details on Facebook 360 Ambisonics Mapping from Angelo Farina”

  1. Hi Bruce

    Really useful, as are all your articles and pluging, but would it also be possible to make a TBE to FOA converter to use FOA effects in a TBE project? Using this from the same Farina article:
    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)

    Or is that only possible in bidule?

    Thanks
    Ed

  2. That’d be a TBE to 2nd order, rather than 1st order Ambisonics, but yes, that is straight-forward to implement. What you can’t do is go from TBE to full 2nd order Ambisonics as m=0 channels are combined.

  3. Glad the YouTube filters have been useful. I do plan on doing the same for Facebook, but the academic year has caught up with me 😉 The TBE audio does seem to be much flatter, anyway, however…

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