On 12/10/2013 02:00 PM, Jörn Nettingsmeier wrote:
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.
sorry, hit "send" without meaning to.
this part of the story is for those listeners who enjoy UHJ over stereo
speakers. now you could argue, why don't we cram Z in so that people who
decode UHJ to ambisonics to a with-height speaker system get some height
information?
the reason is that once you toss 4 components into 2 channels, you can
never perfectly separate them again. there will always be some sort of
"crosstalk". in the case of the X channel, it was found to work pretty
ok and deemed a good compromise, but you can do that 90° phase shift
trick only once. if you cram Z in as well, things stop working altogether.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
_______________________________________________
Sursound mailing list
Sursound@music.vt.edu
https://mail.music.vt.edu/mailman/listinfo/sursound
