Sampo Syreeni wrote:
On 2017-01-09, Stefan Schreiber wrote:
Sorry, correction:
"I must again ask: What does "vbap" actually mean in your question?"
etc.
It refers to Ville Pulkki's dissertation at Aalto University (then
Helsinki University of Technology, fi: Teknillinen korkeakoulu).
http://lib.tkk.fi/Diss/2001/isbn9512255324/isbn9512255324.pdf
Basically VBAP (vector base amplitude panning) is a form of equal
power weighted amplitude panning. Just as your normal stereo panning
law would be, only it's in 3D, over widely varying speaker geometry.
Yes, I basically wrote the same, even linking to some Helsinki source
below dissertation level... :-)
Even if the idea is rather simple, nobody for some reason did it
before Ville, really. Definitely didn't take up the task of
psychoacoustic evaluation of the idea.
Yep.
By Ville's work, it seems to work out better than expected. I wouldn't
be surprised if the likes of Dolby Atmos actually used precisely the
VBAP panning law in order to place their discrete sources.
Probably! Mpeg-H 3DA certainly makes heavy use of VBAP.
The critique I'd have for such panning laws is that they don't really
respect the ambisonic/Gerzon theory, especially at the low frequencies.
Stereophonic panning laws are based on Blumlein's stereo theory, which
in Wittek's opinion is pretty close to sound fields anyway.
In essence, they work, and necessarily would *have* to work in the
high frequency, (ambisonically speaking) high order,sparse array
limit. Which is why they mostly work for common music and speech signals.
Disagreed! ILD panning leads to ITD differences at LF. (According to
Blumlein, not me.)
http://www.hauptmikrofon.de/HW/Wittek_thesis_201207.pdf
In contrast, Blumlein (1933) aimed at a proportional reproduction of
the directional image of
the recorded scene by recreating the original physical auditory cues.
He found that in a
stereophonic setup, the intensity5 differences between the
loudspeakers are converted into
phase differences at the listener’s ears below a certain limit
frequency. Above this frequency,
intensity differences between the loudspeakers would translate to
similar differences between
the ears. Thus both important cues for source localisation would be
synthesised correctly: the
low frequency phase differences and the high frequency intensity
differences.
Blumlein’s ideas are the basis of the summing localisation theory, see
section 3.6.1. They lead
to a computable stereophonic reproduction between the loudspeakers. He
proposed a coincident
microphone setup for capturing intensity differences, consisting of
two bidirectional
microphones at an angle of 90°, which nowadays is known as the
‘Blumlein pair’.
Best,
Stefan
However, they fail to work general speaker arrays fully. Especially at
the lower frequencies. Ambisonically speaking, where we'd go with a
holistic, whole array, directionally averaged velocity decode.
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