New - TOA Converters for YouTube
Posted: 9 June 2016
This is not entirely new, as technically the ambisonic format used by YouTube Spatial Audio is also known as SN3D/ACN and is already supported in our non-free TOA Decoding and TOA Upmixer libraries. But YouTube support for ambisonics is very exciting, so we thought we would add support directly into our free tools.
The third order TOA format that we use ("FuMa") is directly compatible with first order ambisonic B-Format ("Plain Old Ambisonics" or POA) as used back to the 1970s. This is used in many existing systems and microphones. We selected our TOA format for backwards compatibility.
However, this is not what MPEG-H or YouTube have selected as their main ambisonic format. MPEG-H uses N3D and YouTube uses SN3D. N3D and SN3D are slightly different, newer formats designed to handle much higher orders. There are good reasons for this; in fact, internally, much of our software uses a variant of N3D for our "hard maths".
What Does This Mean?
Generally, when you want to export your project to YouTube, you just need to use the simple new "TOA Decoder - To YouTube" decoder while rendering your project to an audio file. Hopefully this will be a familiar way of working from rendering to stereo, binaural, 5.1 and so on.
Keep careful track of what format you are using, because things can go badly wrong if you get confused. We recommend working with our TOA format throughout your project, converting to YouTube Spatial Audio just as a "decoding" step, using the "TOA Decoder - To YouTube" plugin above. Material coming in using YouTube Spatial Audio can be converted to TOA easily using "TOA Injector - From YouTube" and we recommend doing this before applying any TOA processing, to avoid strange results.
At the time of writing, YouTube only supports first order SN3D/ACN, but we've built these plugins at third order, so they produce sixteen channels of audio. To get at just the first order part, use the first four channels and ignore the rest.
The conversions are essentially lossless, but the different gains have implications for noise floor. If you are saving masters to disk in any of these format and they will be converted (or decoded) later we recommend using 24bit audio.
The Rapture3D Universal game/VR engine supports all three formats. FuMa (POA and TOA) is supported from first to third order and N3D/ACN and SN3D/ACN from first to fifth order. Just remember to set the bed "format" correctly so Rapture3D knows what it's dealing with!