Re: [Sursound] Converting 16 mic array recording to B format

[Richard Lee]

Duu.uuh!!  http://parole.loria.fr/DEMAND/DEMAND.pdf states

"the microphones of the array ... are not calibrated with respect to each 
other, and so gain variations are to be expected: we found that the energy 
in some channels is consistently higher than in other channels. Algorithms 
working on this data should compensate for this variation"

ie they haven't a clue what each capsule is doing.

This precludes any attempt at conversion to B-format and also of 
beamforming.

I was hoping this might lead to a discussion about EigenMike and how it 
might be made good enough to record music but this is certainly NOT the 
vehicle.

I can't help feeling they should beg borrow or steal a TetraMic and repeat 
their recordings.

Presently, about all you can say is they have a close bunch of unspecified 
mikes in some sort of horizontal pattern.

Curtiss, if you are after some 'realistic' atmospheric background (and this 
is something TetraMic and properly aligned Soundfields do better than an  
ything else), try ambisonia.com and recordings by John Leonard 
(soundmanjohn), Paul Doombusch, JH Roy & others.

John Leonard's specialty is WW2 aircraft flyovers but he includes a lot of 
airfield noise too :)  He's also got some very realistic street scenes, 
audience noise, applause etc too.

Aaron, you are right about SVD not being much use here as we have multiple 
solutions but I was hoping to dream up something to help S/N at LF.

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Re: [Sursound] Converting 16 mic array recording to B format

[Fons Adriaensen]

On Thu, May 14, 2015 at 06:11:49PM -, Richard Lee wrote:

> Duu.uuh!!  http://parole.loria.fr/DEMAND/DEMAND.pdf states
> 
> "the microphones of the array ... are not calibrated with respect to each 
> other, and so gain variations are to be expected: we found that the energy 
> in some channels is consistently higher than in other channels. Algorithms 
> working on this data should compensate for this variation"
> 
> ie they haven't a clue what each capsule is doing.
> 
> This precludes any attempt at conversion to B-format and also of 
> beamforming.

Indeed. Unless maybe in a very limited frequency range.

Once the phase differences between the capsule signals exceed 180
degrees any synthesized polar pattern will break down and be reduced
to chaos. This determines the upper limit.

On the other side, when wavelenght is much larger than the distance
between the mics, creating anything non-omni requires amplification 
of the small differences between mic signals, and the required gain
increases by 6 db times order for each octave down. If the mic gains 
are not perfectly matched amplified errors will dominate the result. 
This in practice determines the lower limit of the frequency range.
 
> I was hoping this might lead to a discussion about EigenMike and how it 
> might be made good enough to record music but this is certainly NOT the 
> vehicle.

The limits pointed out above are something that Gary Elko has clearly
understood very well (and some others apparently have not). 
The beamforming sofware that comes with the Eigenmike will in general 
not let you do things that depend on unrealistic accuracy of the mic 
gain calibration.

On the upper end the limit for the EM is around 8 kHz. Above that,
the SW will just give you the signal of the single capsule that
is closest to the intended direction of the beam. The polar pattern
above the upper limit will be the one resulting from diffraction
caused by the solid spherical body (this becomes quite directional
in the frequency range considered). This at least produces a clean
signal in the upper octave which is better than the chaotic pattern
a beamformer would produce.

On the lower end, the limits that can be achieved assuming +/- 0.5 dB
gain errors are roughly

  1st order: 50 Hz
  2nd order: 630 Hz
  3rd order: 1.6 kHz
  4th order  2.5 kHz
  
The latter has such a limited frequency range that it's probably
better to forget about it. The EM software wisely doesn't claim
anything above third order.

The result of this, in particular of the lower frequency limits,
is that any higher order directional pattern will have to be a
compromise between on-axis and diffuse-field frequency response.
The requirements for this will depend on the application: a spot
mic or a set of beams intended for surround reproduction. The
tradeoff can be made partly by EQ.

So when using the EM for e.g. orchestral recording using a number
of beams pointed at the various sections of the orchestra, you will
need some rather unconventional EQ for the best results. This will
probably surprise most sound engineers used to the more traditional
way of using a set of normal mics to cover the sections. It may
also put them off. But it is certainly possible to make very good
recordings with the EM. 

Ciao,

-- 
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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Re: [Sursound] Converting 16 mic array recording to B format

[Curtis Alcock]

Thank you everyone who contributed to answering my question. I am now fully 
convinced that using the DEMAND library would be next to useless and not worth 
the work involved in trying to make it (partially) usable. Pity really, as a 
database of everyday noise would be a useful resource – but only if it's done 
properly in the first place.

I am in the process of doing my own field recordings using a Brahma mic (been 
impressed with results so far: birdsong; a very noisy, reverberant restaurant; 
organ playing in a church) but as it will take some time to build up a complete 
library I was looking for some other material I could use, particularly every 
day environments.

Thanks, Richard, for your suggestion of ambisonia.com. I started there but was 
having trouble downloading the torrent files. (The internet access I have here 
(in a shared building) blocks torrent files so I need to download somewhere 
else then transfer.) Will continue to pursue this route.

Thanks again, everyone.

On 14 May 2015, at 19:11, Richard Lee  wrote:

> Duu.uuh!!  http://parole.loria.fr/DEMAND/DEMAND.pdf states
> 
> "the microphones of the array ... are not calibrated with respect to each 
> other, and so gain variations are to be expected: we found that the energy 
> in some channels is consistently higher than in other channels. Algorithms 
> working on this data should compensate for this variation"
> 
> ie they haven't a clue what each capsule is doing.
> 
> This precludes any attempt at conversion to B-format and also of 
> beamforming.
> 
> I was hoping this might lead to a discussion about EigenMike and how it 
> might be made good enough to record music but this is certainly NOT the 
> vehicle.
> 
> I can't help feeling they should beg borrow or steal a TetraMic and repeat 
> their recordings.
> 
> Presently, about all you can say is they have a close bunch of unspecified 
> mikes in some sort of horizontal pattern.
> 
> Curtiss, if you are after some 'realistic' atmospheric background (and this 
> is something TetraMic and properly aligned Soundfields do better than an  
> ything else), try ambisonia.com and recordings by John Leonard 
> (soundmanjohn), Paul Doombusch, JH Roy & others.
> 
> John Leonard's specialty is WW2 aircraft flyovers but he includes a lot of 
> airfield noise too :)  He's also got some very realistic street scenes, 
> audience noise, applause etc too.
> 
> Aaron, you are right about SVD not being much use here as we have multiple 
> solutions but I was hoping to dream up something to help S/N at LF.
> 
> ___
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> account or options, view archives and so on.

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Re: [Sursound] Converting 16 mic array recording to B format

[Paul Hodges]

--On 14 May 2015 11:33 +0100 Curtis Alcock
 wrote:

> Thanks, Richard, for your suggestion of ambisonia.com. I started
> there but was having trouble downloading the torrent files. (The
> internet access I have here (in a shared building) blocks torrent
> files so I need to download somewhere else then transfer.) Will
> continue to pursue this route.

Note that my files from Ambisonia, and John Leonard's, can be
downloaded directly from .

Paul

-- 
Paul Hodges

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Re: [Sursound] Converting 16 mic array recording to B format

[Michael Chapman]

>
> Thanks, Richard, for your suggestion of ambisonia.com. I started there but
> was having trouble downloading the torrent files. (The internet access I
> have here (in a shared building) blocks torrent files so I need to
> download somewhere else then transfer.) Will continue to pursue this
> route.
>

There has been talk, on and off, of 'mirroring' ambisonia.com in a
non-torrent format (the files ar hardly large by 2015 standards ...).

It would certainly be a _big_ plus for some of us.  .  .   (?).

Michael


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Re: [Sursound] Converting 16 mic array recording to B format

[John Leonard]

You can always come direct to me for other stuff as well. I have some music 
recordings made with a TetraMic and an increasing bunch of stuff using the 
ST450. (I know this is heresy, but I've also just acquired Mike Skeet's DPA 
5100. By the way, Mike's not at all well, apparently, and has sold off most of 
his microphone collection, including his Soundfields.)

Regards,

John

Please note new email address & direct line phone number
email: j...@johnleonard.uk
phone +44 (0)20 3286 5942


On May 14, 2015, at 19:11, Richard Lee  wrote:

> John Leonard's specialty is WW2 aircraft flyovers but he includes a lot of 
> airfield noise too :)  He's also got some very realistic street scenes, 
> audience noise, applause etc too.

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Re: [Sursound] Converting 16 mic array recording to B format

[umashankar manthravadi]

dear Curtis
 
I am happy you like the brahma microphone. can you please post some samples on 
ambisonia.com. particularly bird song, as it will be some time before I can go 
out and record (might be able to get some good monsoon recordings in south 
india though, when I shift there) There are many queries about how Brahma works 
for nature recordings, and I am hoping to build a 25 mm capsule version just 
for such use.
 
umashankar
 
> From: curtis.alc...@tiscali.co.uk
> Date: Thu, 14 May 2015 11:33:02 +0100
> To: sursound@music.vt.edu
> Subject: Re: [Sursound] Converting 16 mic array recording to B format
> 
> Thank you everyone who contributed to answering my question. I am now fully 
> convinced that using the DEMAND library would be next to useless and not 
> worth the work involved in trying to make it (partially) usable. Pity really, 
> as a database of everyday noise would be a useful resource – but only if it's 
> done properly in the first place.
> 
> I am in the process of doing my own field recordings using a Brahma mic (been 
> impressed with results so far: birdsong; a very noisy, reverberant 
> restaurant; organ playing in a church) but as it will take some time to build 
> up a complete library I was looking for some other material I could use, 
> particularly every day environments.
> 
> Thanks, Richard, for your suggestion of ambisonia.com. I started there but 
> was having trouble downloading the torrent files. (The internet access I have 
> here (in a shared building) blocks torrent files so I need to download 
> somewhere else then transfer.) Will continue to pursue this route.
> 
> Thanks again, everyone.
> 
> On 14 May 2015, at 19:11, Richard Lee  wrote:
> 
> > Duu.uuh!!  http://parole.loria.fr/DEMAND/DEMAND.pdf states
> > 
> > "the microphones of the array ... are not calibrated with respect to each 
> > other, and so gain variations are to be expected: we found that the energy 
> > in some channels is consistently higher than in other channels. Algorithms 
> > working on this data should compensate for this variation"
> > 
> > ie they haven't a clue what each capsule is doing.
> > 
> > This precludes any attempt at conversion to B-format and also of 
> > beamforming.
> > 
> > I was hoping this might lead to a discussion about EigenMike and how it 
> > might be made good enough to record music but this is certainly NOT the 
> > vehicle.
> > 
> > I can't help feeling they should beg borrow or steal a TetraMic and repeat 
> > their recordings.
> > 
> > Presently, about all you can say is they have a close bunch of unspecified 
> > mikes in some sort of horizontal pattern.
> > 
> > Curtiss, if you are after some 'realistic' atmospheric background (and this 
> > is something TetraMic and properly aligned Soundfields do better than an  
> > ything else), try ambisonia.com and recordings by John Leonard 
> > (soundmanjohn), Paul Doombusch, JH Roy & others.
> > 
> > John Leonard's specialty is WW2 aircraft flyovers but he includes a lot of 
> > airfield noise too :)  He's also got some very realistic street scenes, 
> > audience noise, applause etc too.
> > 
> > Aaron, you are right about SVD not being much use here as we have multiple 
> > solutions but I was hoping to dream up something to help S/N at LF.
> > 
> > ___
> > Sursound mailing list
> > Sursound@music.vt.edu
> > https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, 
> > edit account or options, view archives and so on.
> 
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