Well, we had a lovely time at Sounds in Space again, this year. Thanks to all who contributed to the day (guests, presenters, poster peeps and generous sponsors!). I’ll be uploading and sharing presentations/videos from the day, soon, but in the meantime, here are some pictures (some of the 360 pics are better viewed via the link below).
Tomorrow we’re holding our annual Sounds in Space Research Symposium. This year we’ve decided to stream the entire event on both YouTube and Facebook using binaural audio (well, Ambisonics to binaural as it happens). The event is 9.30am (GMT+1) until around 5.00pm. If you’re interested in watching the events, here’s the links:
It’s looking like it’ll be a great day, so do tune in 🙂
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.
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).
I’ve had a few people ask for me to share the animations from my Surround Audio for VR presentation that I delivered at Sounds in Space this year. I’ve made a video of the powerpoint (30 seconds per slide) so everything can be viewed in context (note there’s no audio, though!). If you weren’t at the event, it goes through both the graphics and audio processing needed to create VR content and shows the limitations, with respect to the inter-aural level (ILD) and time (ITD) differences reproduced by the Ambisonics to Binaural process at varying orders. 8th order Ambisonics does a great job reproducing both the ILD and ITD up to 4kHz.
So, here’s an example (but empty) Reaper project that contains the YouTube binaural filters I measured. You’ll need to use your preferred Ambisonics plug-ins of choice, and I’m assuming FuMa channel ordering etc.. they’ll be remapped by a plug-in.
There is a bundle of JS effects in the folder too, that you’ll need to install (instructions at : http://reaperblog.net/2015/06/quick-tip-how-to-install-js-plugins/) which allow for:
- Ambisonic Format Remapping (FuMa -> ambiX)
- Ambisonic Field Rotation
- Multi-channel Meter
YouTube have now released the official ones they use (but in individual speaker format….not the most efficient way of doing it!), so it’ll be interesting to compare!
As described in a previous post, the ReaVerb plug-in is filtering W, X, Y and Z with a pair of HRTFs which are then simply summed to create the Left and Right feeds.
UPDATE : 4th May 2016 – I’ve added a video using the measured filters. This will be useful for auditioning the mixes before uploading them to YouTube.
So, I’ve been experimenting with YouTube’s Ambisonic to Binaural VR videos. They work, sound spacious and head tracking also functions (although there seems to be some lag, compared to the video – at least on my Sony Z3), but I thought I’d have a dig around and test how they’re implementing it to see what compromises they’ve made for mobile devices (as the localisation could be sharper…)
Cut to the chase – YouTube are using short, anechoic Head Related Transfer Functions that also assume that the head is symmetrical. Doing this means you can boil down the Ambisonics to Binaural algorithm to just four short Finite Impulse Response Filters that need convolving in real-time with the B-Format channels (W, X, Y & Z in Furse Malham/SoundField notation – I know YouTube uses ambiX, but I’m sticking with this for now!). These optimisations are likely needed to make the algorithm work on more mobile phones.
So, last week Google enabled head (phone!) tracked positional audio on 360 degree videos. Ambisonics is now one of the defacto standards for VR audio. This is a big moment! I’ve been playing a little with some of the command line tools needed to get this to work, and also with using Google PhotoSphere pics as the video as, currently, I don’t have access to a proper 360 degree camera. You’ll end up with something like this:
So first, the details. Continue reading “YouTube, Ambisonics and VR”