4.6 The Ambisonic Method

One of the challenges facing spatial audio designers is how to spatialise and mix when the full installation is not available to mix on. The other related problem is how to re-spatialise a virtual scene mixed for one type of speaker layout, onto a different one. Spat Revolution can provide solutions to these problems.

In order to get a rough idea of how a spatialised scene might sound on a particular speaker configuration - including the gaps between the speakers, and the characteristic of a chosen panning type - then the binaural 3D headphone monitor module can be used. It can give a headphone representation of a channel based virtual scene. It has its limitations though so the binaural monitor module should not be relied upon for all mix decisions. It is there as a quick way to ‘dip’ into the virtual scene but only has the spatial resolution of the number of speakers in the channel based stream.

A better way to get a high resolution 3D audio image would be to create a binaural room in parallel with a channel based room. This will binauralise the sources and their virtual acoustics in a room with no speakers - this is the best binaural experience Spat Revolution provides - although of course it is still limited to headphones only (see section 5.1).

Perhaps the most practical solution, comes from the ambisonic technology which is at the heart of Spat Revolution, and in fact behind the binaural rendering just described. Ambisonics, as we are about to discover, is an encoded audio format that gives us the possibility to decode consistent 3D spatial information onto any channel based / speaker compatible format. Because Spat Revolution is fundamentally a High Order Ambisonics engine, it gives a designer the possibility to keep working on the spatial parameters of a complex virtual audio scene and monitor on whatever speaker or headphone setups she might have access to - such as binaural, 5.1 surround, simple Quad, stereo and so on. The spatialisation should translate more or less intact after decoding. Of course, there’s still tuning work to do in practice, but it is much better than imagining how things are going to sound, and further more - is a very interesting application of an audio technology with quite a legacy behind it. Time for a quick introduction to Ambisonic technology.