Re: [Sursound] Array for sound field recording and extend the sound image

[Bo-Erik Sandholm]

An open paper on directional mics
http://www.iwaenc.org/proceedings/2001/main/data/buck.pdf

I had a idea that I could use 2 close mounted mics (o) for Upper frequency 
ranges and a longer distance between 2 additional elements (x) to have  better 
signal to noise ratio for the lower frequency band, would that be practical? 
Then mix the 2   hi o and low x  frequency signals.

(x) (o)(o)(x)  4 omni mics for a figure 
of 8 pattern mic, maybe mounted on a plate according to 

I have seen  a DIY differential mic based on the blumlein principle  
http://www.williamsonic.com/DipoleMic/index.html

A advanced way of doing it:-)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677264/

- Bo-Erik






-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Tim Collins
Sent: den 8 januari 2013 18:54
To: Surround Sound discussion group
Subject: Re: [Sursound] Array for sound field recording and extend the sound 
image

You can make a velocity microphone by subtracting two closely spaced omnis. I 
saw a paper on making ambisonic recordings like this a couple of years ago:
http://www.aes.org/e-lib/browse.cfm?elib=15389
The problems, though, are spatial aliasing at high frequencies and lack of 
sensitivity at low frequencies. These would both need addressing in a practical 
system.

Best wishes
Tim


    Dr. Tim Collins
    Electronic, Electrical and Computer Engineering
    University of Birmingham
    Edgbaston, Birmingham, B15 2TT, UK
    www.eee.bham.ac.uk/collinst 
 




-Original Message-
From: Mike Felton [mailto:mjfel...@gmail.com] 
Sent: 08 January 2013 00:21
To: Surround Sound discussion group
Subject: Re: [Sursound] Array for sound field recording and extend the sound 
image

>The mics are omnis

It might be stating the obvious here but how would you get ANY directional 
information out of four OMNI mics close together? :-)

Surely to get a fig-8 response you need two CARDIODS back to back (one of which 
is polarity reversed obviously).

Mike Felton
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Re: [Sursound] Array for sound field recording and extend the sound image

[Peter Lennox]

HI, the front-back reversals problem isn't peculiar to ambisonics - it can 
sometimes happen in real life (most often, though not always, in a symmetrical 
space) and is well known in the laboratory. It's really a subset of the 'cones 
of confusion' problem, which Batteau proposed that Pinnae effects help with, 
and Wallach proposed head movements help with - and I'd say you get best 
results with both.
Since ambisonics, especially in lower orders, actually homogenises  potential 
pinnae cues (eg using multiple sources to produce a simulation of a plane wave 
from a single source), then 'search behaviour' - small head movements to 
produce different sets of pinnae cues- works less well than for real 
environments; movements have to be grosser, and for longer.
Higher orders help, some kind of processing for high frequencies (Harpex, for 
instance) might help. I've even cheated with this and used a precedent (about 
7ms), bandwidth limited, amplitude limited, version of a target source simply 
routed into a single speaker - sort of an infinite order applied to transients. 
This last removes some of the actual  reversals that you get ion a large array 
with off-centre listeners

cheers

Dr. Peter Lennox

School of Technology,
Faculty of Arts, Design and Technology
University of Derby, UK
e: p.len...@derby.ac.uk 
t: 01332 593155

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Chenrilin
Sent: 09 January 2013 03:29
To: sursound@music.vt.edu
Cc: Zhangdeming
Subject: Re: [Sursound] Array for sound field recording and extend the sound 
image

http://www.huawei.com 

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Re: [Sursound] Array for sound field recording and extend the sound image

[Dave Malham]

Hi Tim,
Indeed, SNR is poor at low frequencies for this sort of technique as
it relies on the phase difference between the two capsules as produced
by their separation. The separation can't be too large as once it gets
over half a wavelength the phase starts wrapping around but this means
that at low frequencies the difference is tiny and requires a lot of
amplification (cf. the 6dB rise in response with frequency that
someone else mentioned). This results in poor SNR and worsening
susceptibility to capsule variances as the frequency goes down. If you
can cope with the extra complexity, using more than one set of
capsules with different spacings to cover different frequency ranges
is a good idea...

Dave

On 9 January 2013 00:15, David Pickett  wrote:
> At 11:54 08-01-13, Tim Collins wrote:
>
>>You can make a velocity microphone by subtracting two closely spaced omnis.
>
> I seem to recall that Blumlein did this and also found that the s-n ratio
> was poor.
>
> David
>
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-- 
As of 1st October 2012, I have retired from the University, so this
disclaimer is redundant


These are my own views and may or may not be shared by my employer

Dave Malham
Ex-Music Research Centre
Department of Music
The University of York
Heslington
York YO10 5DD
UK

'Ambisonics - Component Imaging for Audio'
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Re: [Sursound] Array for sound field recording and extend the sound image

[Chenrilin]

http://www.huawei.com

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Re: [Sursound] Array for sound field recording and extend the sound image

[David Pickett]

At 11:54 08-01-13, Tim Collins wrote:

>You can make a velocity microphone by subtracting two closely spaced omnis.

I seem to recall that Blumlein did this and also found that the s-n 
ratio was poor.


David

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Re: [Sursound] Array for sound field recording and extend the sound image

[Tim Collins]

You can make a velocity microphone by subtracting two closely spaced omnis. I 
saw a paper on making ambisonic recordings like this a couple of years ago:
http://www.aes.org/e-lib/browse.cfm?elib=15389
The problems, though, are spatial aliasing at high frequencies and lack of 
sensitivity at low frequencies. These would both need addressing in a practical 
system.

Best wishes
Tim


    Dr. Tim Collins
    Electronic, Electrical and Computer Engineering
    University of Birmingham
    Edgbaston, Birmingham, B15 2TT, UK
    www.eee.bham.ac.uk/collinst 
 




-Original Message-
From: Mike Felton [mailto:mjfel...@gmail.com] 
Sent: 08 January 2013 00:21
To: Surround Sound discussion group
Subject: Re: [Sursound] Array for sound field recording and extend the sound 
image

>The mics are omnis

It might be stating the obvious here but how would you get ANY directional 
information out of four OMNI mics close together? :-)

Surely to get a fig-8 response you need two CARDIODS back to back (one of which 
is polarity reversed obviously).

Mike Felton
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Re: [Sursound] Array for sound field recording and extend the sound image

[Michael Chapman]

>
> Thanks very much. You are so kind. I will have a try as your suggestion.
>
> Best regards,
>   
>   Rilin
> Chen

Do let us know with what results !

These type of problems are usually a learning experience for us all 

Best of luck,

Michael


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Re: [Sursound] Array for sound field recording and extend the sound image

[Chenrilin]

>Hi,

>   Seems likely then that the problem is related to the usual "in

>head" problem that many (maybe even most) people people have with

>simple, non matched HRTF based systems, whether driven from decoded

>Ambisonic signals or from binaurally recorded (dummy head) material.

>There's been a lot of work on this (just search the AES library, for

>instance) and there have been many suggestions for solving this but,

>in my opinion, the only one which has anything like a chance for

>solving the problem for the majority of listeners is to add head

>tracking to the system. This is because if the soundscape stays locked

>to the reference frame of your head (as happens without head

>tracking), it is _very_ difficult to convince your perceptions that it

>is anything but in your head and therefore locking the soundscape to

>the external fixed reference plane by using headtracking instead makes

>it much more natural to perceive it as external. This is even more

>important even than having HRTF's that are the same as, or closely

>matched to, your own (though such individualised responses do help).

>Strong visual cues can also help and in some cases will be almost as

>good at moving the perceived reference frame to the external world as

>you get with headtracking - though this is _very_ dependent on the

>particular circumstances.

Thanks very much. You are so kind. I will have a try as your suggestion.

Best regards,

Rilin Chen


华为技术有限公司 Huawei Technologies Co., Ltd.
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Re: [Sursound] Array for sound field recording and extend the sound image

[Mike Felton]

>The mics are omnis

It might be stating the obvious here but how would you get ANY directional
information out of four OMNI mics close together? :-)

Surely to get a fig-8 response you need two CARDIODS back to back (one of
which is polarity reversed obviously).

Mike Felton


On 7 January 2013 23:19, Fons Adriaensen  wrote:

> On Mon, Jan 07, 2013 at 03:12:26PM -0800, Aaron Heller wrote:
>
> > Without more details, it hard to speculate about problems, but I'll note
> > that subtracting the outputs of two omnis to get a fig-8 response will
> > result in a frequency response that rises 6dB/octave with a 90 degree
> phase
> > shift relative to the sum.  Unless that is corrected, these signals are
> not
> > suitable for B-format.
>
> Exactly, and it could explain the strange effects in the binaural
> format. But the OP didn't provide any details about the processing
> he uses to obtain B-format.
>
> 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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-- 
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+44 7595 367 228
+44 20 8876 6122
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Re: [Sursound] Array for sound field recording and extend the sound image

[Fons Adriaensen]

On Mon, Jan 07, 2013 at 03:12:26PM -0800, Aaron Heller wrote:

> Without more details, it hard to speculate about problems, but I'll note
> that subtracting the outputs of two omnis to get a fig-8 response will
> result in a frequency response that rises 6dB/octave with a 90 degree phase
> shift relative to the sum.  Unless that is corrected, these signals are not
> suitable for B-format.

Exactly, and it could explain the strange effects in the binaural
format. But the OP didn't provide any details about the processing
he uses to obtain B-format.

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] Array for sound field recording and extend the sound image

[Aaron Heller]

Without more details, it hard to speculate about problems, but I'll note
that subtracting the outputs of two omnis to get a fig-8 response will
result in a frequency response that rises 6dB/octave with a 90 degree phase
shift relative to the sum.  Unless that is corrected, these signals are not
suitable for B-format.


On Mon, Jan 7, 2013 at 11:31 AM, Martin Leese <
martin.le...@stanfordalumni.org> wrote:

> Chenrilin wrote:
>
> > Hello, all
> > I have designed an array of four microphones to get B-format signal.
> ...
> > Then I decoded
> > them to get the
> > feeding signal for four loudspeakers, and used HRTFs to get the left and
> > right signal for headphone.
> >
> > 1.   Furthermore, the experiment is made that a person was walking
> > around the array and say
> > something in an office. After processed by the method above, I find
> there is
> > a problem that
> > the speech sounds like a person talking and moving around my head but
> very
> > near to my ears
> > and head. What is the main reasons for this problem?
>
> What happens when you decode a walkaround
> downloaded from Ambisonia.com?  That is to
> say, a walkaround recorded with somebody
> else's mic.
>
> This would allow you to determine whether the
> problem is with your decoder, or with the way
> you calculate your B-Format components.
>
> Regards,
> Martin
> --
> Martin J Leese
> E-mail: martin.leese  stanfordalumni.org
> Web: http://members.tripod.com/martin_leese/
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Re: [Sursound] Array for sound field recording and extend the sound image

[Martin Leese]

Chenrilin wrote:

> Hello, all
> I have designed an array of four microphones to get B-format signal.
...
> Then I decoded
> them to get the
> feeding signal for four loudspeakers, and used HRTFs to get the left and
> right signal for headphone.
>
> 1.   Furthermore, the experiment is made that a person was walking
> around the array and say
> something in an office. After processed by the method above, I find there is
> a problem that
> the speech sounds like a person talking and moving around my head but very
> near to my ears
> and head. What is the main reasons for this problem?

What happens when you decode a walkaround
downloaded from Ambisonia.com?  That is to
say, a walkaround recorded with somebody
else's mic.

This would allow you to determine whether the
problem is with your decoder, or with the way
you calculate your B-Format components.

Regards,
Martin
-- 
Martin J Leese
E-mail: martin.leese  stanfordalumni.org
Web: http://members.tripod.com/martin_leese/
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Re: [Sursound] Array for sound field recording and extend the sound image

[Dave Malham]

On 7 January 2013 02:08, Chenrilin  wrote:
>>Do you get the same problem if you playback through four loudspeakers, or
>
>>is it only after HRTF manipulation ?
>
>>* Does the decoding work on speakers (without HRTF) ?

>
> The mics are omnis. And it can work on speakers well. So I think
>  X and Y computed is exactly for decoder.
>

Hi,
   Seems likely then that the problem is related to the usual "in
head" problem that many (maybe even most) people people have with
simple, non matched HRTF based systems, whether driven from decoded
Ambisonic signals or from binaurally recorded (dummy head) material.
There's been a lot of work on this (just search the AES library, for
instance) and there have been many suggestions for solving this but,
in my opinion, the only one which has anything like a chance for
solving the problem for the majority of listeners is to add head
tracking to the system. This is because if the soundscape stays locked
to the reference frame of your head (as happens without head
tracking), it is _very_ difficult to convince your perceptions that it
is anything but in your head and therefore locking the soundscape to
the external fixed reference plane by using headtracking instead makes
it much more natural to perceive it as external. This is even more
important even than having HRTF's that are the same as, or closely
matched to, your own (though such individualised responses do help).
Strong visual cues can also help and in some cases will be almost as
good at moving the perceived reference frame to the external world as
you get with headtracking - though this is _very_ dependent on the
particular circumstances.

   Best regards,
   Dave Malham


As of 1st October 2012, I have retired from the University, so this
disclaimer is redundant


These are my own views and may or may not be shared by my employer

Dave Malham
Ex-Music Research Centre
Department of Music
The University of York
Heslington
York YO10 5DD
UK

'Ambisonics - Component Imaging for Audio'
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Re: [Sursound] Array for sound field recording and extend the sound image

[Chenrilin]

>Do you get the same problem if you playback through four loudspeakers, or

>is it only after HRTF manipulation ?


>We'll need a bit more information.



>* Are the mics omnis, or directional ? If directional, what

>  are the directions ?



>* How exactly to you compute X and Y frm the mic signals ?



>* Does the decoding work on speakers (without HRTF) ?



The mics are omnis. And it can work on speakers well. So I think

X and Y computed is exactly for decoder.




华为技术有限公司 Huawei Technologies Co., Ltd.
[Company_logo]

Phone:
Fax:
Mobile:
Email:
地址：深圳市龙岗区坂田华为基地 邮编：518129
Huawei Technologies Co., Ltd.
Bantian, Longgang District,Shenzhen 518129, P.R.China
http://www.huawei.com

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Re: [Sursound] Array for sound field recording and extend the sound image

[Fons Adriaensen]

On Sun, Jan 06, 2013 at 09:18:43AM +, Chenrilin wrote:
> Hello, all
> I have designed an array of four microphones to get B-format signal. The 
> coordinates of mics
> are mic1 (-d/2,0), mic2 (d/2,0), mic3 (0, d/2), mic4 (0,-d/2),and d is about 
> 18mm.Every opposite
> pair can be composed into a first order differential array and get a pattern 
> of figure 8. So the X
> component can be got from mic1 and mic2, the Y  component can be get from 
> mic3 and mic4.
> The W component equals to the mean of signals from four mics. Then I decoded 
> them to get the
> feeding signal for four loudspeakers, and used HRTFs to get the left and 
> right signal for headphone.
> 
> 
> 1.   Furthermore, the experiment is made that a person was walking around 
> the array and say
> something in an office. After processed by the method above, I find there is 
> a problem that
> the speech sounds like a person talking and moving around my head but very 
> near to my ears
> and head. What is the main reasons for this problem? Is there any suggestion 
> to make it sounds
> much further from the ears and head.
> 
> 2.   Do I need to add the early reflection and late reverberation to the 
> four loudspeakers? In my
> understanding, the recording signal of array has included the reflection and 
> late reverberation
> signal of the office. If add another reflection signal to the feeding signal 
> of loudspeakers, they
> will contain two kind of reflection signal. Is my understanding right? 
> Apologize for this simple question.

We'll need a bit more information.

* Are the mics omnis, or directional ? If directional, what
  are the directions ?

* How exactly to you compute X and Y frm the mic signals ?

* Does the decoding work on speakers (without HRTF) ?

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] Array for sound field recording and extend the sound image

[Michael Chapman]

> Hello, all
[ ... ]
> The W component equals to the mean of signals from four mics. Then I
> decoded them to get the
> feeding signal for four loudspeakers, and used HRTFs to get the left and
> right signal for headphone.
>
>
> 1.   Furthermore, the experiment is made that a person was walking
> around the array and say
> something in an office. After processed by the method above, I find there
> is a problem that
> the speech sounds like a person talking and moving around my head but very
> near to my ears [ ... ]

Do you get the same problem if you playback through four loudspeakers, or
is it only after HRTF manipulation ?

(I cannot see how it would cause this, but: Have you controlled to see if
W is at the correct level compared with X and Y (depends a lot on the
polar pattern of your mic's). Probably would need to analyse some
recordings of 'point' sources to check that.)

Michael


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