Fons Adriaensen wrote:
On Sun, Dec 06, 2015 at 06:48:25PM +0000, Stefan Schreiber wrote:
Fons Adriaensen wrote:
No matter what type of mic you place behind such a tiny hole, it
will pick up the pressure at that tiny hole. So apart from
diffraction effects the result will be omni.
But the pressure will come from -90º to +90º, at least mainly? If
so, the capsule "view" is 180º, not 360º. (Case as shield)
It acts as a 'shield' only at higher frequencies, as you
can see in the plots.
And then there is the peak at 180 degrees, the result
of all parts of the wave travelling around the sphere
arriving there exactly in phase.
But your plots surely don't apply directly to the Ozo sphere, which is
packed with electronics inside? (s. Nokia's videos.)
The word "case" includes the interior of the sphere, which is not hollow.
Your plots refer to an empty sphere, don't they?
Serious question: Is this not (more or less) a cardioid response?!
Take for example the 8kHz response, which is the most
directive one in the set. It's something like 3.5 dB
down at 90 degrees. Apart from the narrow peak at the
back, that's subcardioid.
See above. We currently don't know the exact frequency responses...
This produces a usable fig-8 up to 1 kHz or so (with lower
frequencies requiring additional gain). Above that, chaos
takes over. Using more mics (e.g. the four frontal ones
minus the four at the back) will not improve things.
...
But if it IS a hedgehog based mike, this is no issue.
It is. If the video from the OZO is viewed on VR glasses
(so the viewer can face *any* direction and even tilt his
head sideways) then the audio needs to be in a format
that has no preferred directions and that can be rotated
to any attitude, in order to follow the viewer's motions.
And? This is exactly the case here. (IRT cross in two dimensions and the
8-channel hedgehog in the described cuboid form are isotropic. All 12
microphone stereo angles are 90º. A cube is a Platonic solid, "as
everybody knows".)
The 'hedgehog' doesn't produce anything like that, nor
is it meant to.
It does and is meant to!
As Theile says himself in the paper, it
is not designed to provide non-horizontal directional
information, but to fill the top hemisphere with
uncorrelated signals. This is more or less the opposite
of what would be required.
< Where > does he say this, in this paper?
See also:
http://www.hauptmikrofon.de/stereo-3d/3d-audio/67-ortf-3d-microphone-technique-for-3d-ambience-recording
Best,
Stefan
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