On 12/10/2013 08:20 AM, Bearcat M. Şándor wrote:
Is there a technical reason why z is never included in UHJ recordings?
yes.
2-channel UHJ is meant as a stereo-compatible encoding in two channels
(let's ignore the 3 and 4 channel extensions of UHJ for now), that
should be playable over a standard stereo triangle.
on stereo speakers, you can obviously reproduce left-right localisation
easily. so you need the respective ambisonic components W and Y to go
into UHJ. if the story ended here, UHJ would just be a mid-side matrix.
turns out you can also get _some_ sense of rear localisation (or at
least enough confusion so that you don't localise it in front) if the
two speakers play back a heavily correlated signal but with extreme
phase shift (between 90 and 180° out of phase). so X (the front mminus
back component in ambisonics) goes in as well, with some rather
heavy-handed phase trickery.
Z represents the up minus down component. there is no way to reproduce
that with two speakers on a horizontal plane, and there exists no handy
psycho-acoustic loophole as for X. hence, Z is dropped completely.
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