"Joern will probably answer your question and provide some good
arguments for his opinion. But I do share his view on this (Eigenmike)"


Hi Fons,

Thanks for your indepth reply which is very interesting, so it seems that the 
microphone is still not a perfect solution for HOA recording and requires some 
highly technical tinkering before it will give half decent results. I have only 
ever heard two brief pieces of audio recorded with the mic so i am not 
qualified to comment on it, however the demo on you tube is quite good and 
demonstrates the focussing (beamforming) capability of the mic,one of the 
points that you were stating. Alas i don't have th 20,000 or so to buy one so 
will have to stick with the Soundfield and other measures.

Thanks, Paul Power



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Sent: Wednesday, 12 June 2013, 17:00
Subject: Sursound Digest, Vol 59, Issue 12
 

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Today's Topics:

   1. Re: Eigenmike (Fons Adriaensen)


----------------------------------------------------------------------

Message: 1
Date: Tue, 11 Jun 2013 22:02:12 +0000
From: Fons Adriaensen <f...@linuxaudio.org>
Subject: Re: [Sursound] Eigenmike
To: sursound@music.vt.edu
Message-ID: <20130611220212.gb32...@linuxaudio.org>
Content-Type: text/plain; charset=us-ascii

On Tue, Jun 11, 2013 at 12:44:01PM +0100, Paul Power wrote:

> Hi Jorn,
> Why do you say that you would not want to use the Eigenmike for musical 
> recordings? 

(pre scriptum: please do not copy the entire digest when 
replying...)

Joern will probably answer your question and provide some good
arguments for his opinion. But I do share his view on this.
Of all the musical recordings made using the Eigenmike I've heard
so far there were none that I really liked. It's all too easy to
get carried away by the initial quite spectacular surround effect,
but once that wears off, in all cases I want to reach for some EQ.
And using EQ usually improves things, but never to the point that
the result is really OK.

When you use a recording technique such as Blumlein, XY, MS, or ORTF 
everything depends on how well the mics preserve their polar pattern
in function of frequency - or their frequency response in function
of direction - for the simple reason that almost all sources will
be off-axis. That's an entirely different situation compared to
multi-mic techniques, where such things matter much less, and it's
why people tend to use high quality expensive mics in such a role.

When using the Eigenmic (or a first order tetrahedral), you're in
the same situation. You will use either virtual directional mics
or Ambisonic components which are polar patterns as well. Simple
fact is that with the current state of the art these synthesised
patterns are not really what they should be - they are only correct
over a rather limited frequency range which gets narrower as either
Ambisonic order or directivity goes up. Which in the end means you
can either get the direct sound right, or the diffuse (reverb) part,
but not the two at the same time. Which is why EQ fails to correct
things.

In some applications that is not a problem, for example when you
need some virtual spot mics to follow one or a few actors on a film
set or stage. But when the result depends on capturing sound from
all directions in a balanced way - as it does for music recordings 
which include e.g. the concert hall acoustics as well, this is a
real problem. 

There are currently two SW apps for processing the Eigenmic signals
into either a set of directional 'spot' mics or into third order
Ambisonics: the original SW coming with the Eigenmic, and the one
developed by Farina's team here in Parma. While I'm not personally
involved in the latter, I'm following that project closely. But so
far neither of them have things as right as they could be. Part of
the problem may be that even while the Eigenmic capsules are of
very high quality, the remaining random differences in sensitivity
and frequency response are still too large to allow accurate higher
order processing without individual calibration. And until someone
finds a better method than renting an anechoic room for half a day,
such calibration is an expensive exercise.

Earlier today I've been listening to some organ recordings made using
the Eigenmic and processed into 3rd order Ambisonics. This is one of
the applications that work reasonably well - frequency response errors
on organ sounds are much more forgiving than on e.g. a string quartet,
or voices. But I found the difference between a 1st order decode and
a 3rd order one rather marginal while it is normally quite easy to hear
that difference. Which probably means that higher order components are
not as accurate as they should be.

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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