Development and application of a stereophonic multichannel recording technique for 3D Audio and VR
by Helmut Wittek, 2016
Fig. 1 above: ORTF-3D arrangement, in a windscreen with the cover removed
Recording engineers who work with 3D sound face a difficult task when choosing a suitable recording technique. The number of channels is greater than with playback systems that operate only in the horizontal plane, so the complexity increases as well.
When a customer demands 3D audio rather than conventional 5.1 surround it may be tempting to apply solutions that are overly simple. But when a 3D recording has been made well, using a suitable recording technique, the advantages are impressively audible.
One recording method for all 3D formats?
There are various 3D audio playback systems, so the recording techniques that work best for each of them will naturally be different. For soundfield synthesis systems, multichannel microphone arrays can be a solution, while for 3D stereo, stereophonic miking techniques are the norm.
For binaural reproduction in the simplest case, a dummy head can be used.
But all these systems share one requirement when recording complex, sustained sound sources such as ambient sound: Stereophonic techniques must be used, because they alone offer both highquality sound and high channel efficiency. It is impossible or inefficient to reproduce in high quality the sound of a large chorus, for example, or the complex, ambient sound of a city street, by compiling single point sources recorded with separate microphones.
In the same way, multichannel microphone arrays for soundfield synthesis, such as higher-order Ambisonics ("HOA") or wavefield synthesis, fall short in practice because their channel efficiency and sonic quality are too low. If on the other hand the number of channels is reduced, e.g. with firstorder Ambisonics, the spatial quality becomes burdened with compromise.
For binaural playback, the dummy head technique is clearly the simplest solution-but it does not, in itself, produce results compatible with virtual reality glasses, in which the binaural signals must respond to user's head motions. This is possible only through the "binauralization" of a stereophonic array-a technique that is already well established in audio for games.
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