Politis Archontis wrote:
Hi Steven,
(hurried reply on the go) the numbers were for 17cm diameter (8.5cm radius).
You also get around 15-18dB SNR improvement just by combining that many
microphones, that’s still included in that simulation.
I wasn’t saying that the device is not good or useful, apart from the video,
you can do a lot of useful stuff with that many microphones, binaural
rendering, beamforming etc.. I was saying that it’s not a very good HOA
microphone with these specs.
But this mike will be used to record (mostly) background (and
on-location) scene audio - and not to record some complete film track!
As Steven says most of the audio will be mixed in the studio.
It would be nice to compare the Sonicam SA mike solution later to say
the Ozo Vr camera. (I still don't know how "Ozo 8-capsule spherical
audio" is supposed to work...)
So a mathematical "camera audio review" is maybe interesting but will be
way too negative - because the intended use is not to record music. At
least not on its own.
(A SF mike can do this and an eigenmike to a certain degree.)
Best,
Stefan
P.S.: Why can't we assembled here on the "Ambisonics list" (coughing) be
a little bit more friendly to the people actually applying
Ambisonics? ;-)
On 30 May 2017, at 16:26, Steven Boardman
<boardroomout...@gmail.com<mailto:boardroomout...@gmail.com>> wrote:
Hi Archontis
The size is 170mm diameter not radius.
They also state the capsules are in arrays of 16, so 4 arrays of 16 capsules.
Looking at the camera though, I can’t work it out….
The also said:
'The noise and frequency respond i quote is for individual mic. We have noise
reduction algorithm to improve 15db in total compared to each mic.
For frequency respond, we are using the EQL process，reach to the “flat".'
I knew that it wouldn’t be well behaved in the entire range, and as a
consequence could not be relied on for a quality full bandwidth recording.
This isn’t always the point though. As it could still be used as a reliable
reference for the most crucial of frequency ranges, the voice.
As long as it can record dialogue, one can reconstruct with ADR. It’s just
wether it is intelligible, and accurate enough spatially.
90% of audio for films is done in post anyway, especially dialogue.
It includes 6 camera’s (and the footage isn’t too bad), so to me it seems like
a bargain. I just need to hear the audio first. Otherwise it maybe better just
to spend it all on a camera.
What has been mentioned by Fons, and yourself is obviously completely true, but
we all know in practice it is probably worse. Even more reason to hear their
3rd order render. Of course 5th is a dream…..
While we are on the maths;
For 3rd order, and with the minimum amount of capsules, how small would the
sphere need to be, for a range up to say 16kHz, or maybe even 18kHz?
Am I correct in assuming that the distance between the capsules needs to be
less than half the highest wavelength represented?
Best
Steve
On 27 May 2017, at 23:18, Politis Archontis
<archontis.poli...@aalto.fi<mailto:archontis.poli...@aalto.fi>> wrote:
Hi Steven,
as Fons mentioned before such an array will have trouble to deliver proper HOA
components at a useful range. Running a simple simulation here for R=17cm and
assuming perfect matched microphones and perfectly (uniformly) arranged,
spatial aliasing starts to become serious at 4.5kHz. Assuming that the encoding
filters allow some noise amplification, eg 15dB, to get some more usable low
frequencies:
2nd order is well behaved at 200 Hz - 5.5 kHz
3rd order at 600 Hz - 5 kHz
4th order at 1 kHz - 4.5 kHz
5th order at 1.5kHz - 4 kHz
Since the microphones will have some unidealities, and their placement is not
uniform as far as I can see, the actual performance can be worse than that,
depending how much the encoding filters are optimized for the setup or not. And
again that’s assuming 15dB of more noise (frequency-dependent) at the HOA
signals than the microphones, which may be a problem at many recordings. Less
permitted noise on the other hand means that all the low limits for all orders
go up, hence, even smaller usable ranges.
If one wishes to capture spatial sound in a HOA format, instead of having a
device that tries to do everything, it would make more sense to have a separate
camera, and a dedicated HOA microphone since it requires careful optimization
for that purpose.
Regards,
Archontis Politis
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