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 🙂 :

Update: September 2017 (from http://pcfarina.eng.unipr.it/TBE-conversion.htm)

NEW Version of the Tools: WigWare AmbiX, FuMa and TBE Tools Sept. 2017 Update

Facebook have updated TBE to remove the ‘R’ component from channel 4.  This is important as, before it was removed, it was impossible to go from TBE to 1st order Ambisonics (for Youtube etc.).  The new details are excellently discussed on Angelo’s webpage which can be found at http://pcfarina.eng.unipr.it/TBE-conversion.htm

TBE(1) =  0.488603 * Ambix(0); W
TBE(2) = -0.488603 * Ambix(1); Y
TBE(3) =  0.488603 * Ambix(3); X
TBE(4) =  0.488603 * Ambix(2); Z
TBE(5) = -0.630783 * Ambix(8); U
TBE(6) = -0.630783 * Ambix(4); V
TBE(7) = -0.630783 * Ambix(5); T
TBE(8) =  0.630783 * Ambix(7); S

Note that going from TBE to horizontal 2nd order FuMa is unchanged (useful for driving my Irregular Ambisonics Decoders 😉

A good timeline and discussion of the issues, and why Facebook changed the encoding, can be found here.

Older Information, pre V2.2 of Facebook Spatial Workstation.

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).

 

7 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…

  4. Hi Bruce, very important info.
    My formulas for conversion from Ambisonics to TBE were wrong, as I derived them from the behaviour of the Spatialser plugin, which also generates wrong TBE signals, with elevation completely messed up.
    I just updated my web page, now it contains the correct formulas. So please, you should fix also this page and your JS plugin!
    More info here:
    https://www.facebook.com/groups/audio360support/permalink/2053591944871670/

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