sursound: Level alignment of Soundfield microphones

[farina]

Yesterday I recorded a piano concert at the Teatro Comunale of Ferrara with
my Soundfield MKV microphone and my new multi-channel DAT (SONY PC-208),
employing the latter in the 4-channels mode.
At the beginning, I recorded 30s of the special test signal generated from
the Soundfield control unit: it is an 1 kHz tone, which is steady on channel
W, and intermittent on the X,Y and Z.
Today I have transferred the recording on my PC (through the Layla sound
board), and I discovered that the reference signals have different
amplitudes: the W signal is 2.2 dB lower than X, Y and Z. I have checked the
DAT, but I discovered that this level mismatch comes from the Soundfield
itself.
Now, the question is: what should be the output levels of the reference
signals? Does the W channels have to be exactly 3 dB lower than the other 3,
or does it have to be at the same level? It depends on the fact that the 3
dB attenuation is before or after the electronic signal generator inside the
Soundfield... The manual says that the reference signal should be 0 dBm on
all the 4 channels...
Is it possible to re-calibrate the output levels of the Soundfield
microphone (without sending it back to the UK)?
Can anyone help me?
Bye!

Angelo Farina
Dipartimento di Ingegneria Industriale
Universita' di Parma
Via delle Scienze - 43100 PARMA (Italy)

You can reach me at:
E-MAIL: mailto:***@pcfarina.eng.unipr.it
HTTP://pcfarina.eng.unipr.it
tel. [phone] - fax [phone]
-----Original Message-----
From: Richard Elen <***@igc.org>
To: Kaleita, David (D.L.) <***@visteonet.com>;
'***@lists.uoregon.edu' <***@lists.uoregon.edu>
Date: Friday, November 20, 1998 23:46
Subject: Re: sursound: G-Format (with HEIGHT) de factor standard
alreadyset??!!

SoundField has introduced its 5.1 microphone system. This allows recording
and broadcast engineers to facilitate a complete 5.1 mix from a single
multiple element microphone...
I wonder...
1) What angular dimensions are these derived speaker feed signals at?
and
2) How is the W signal incorporated?
Does anyone have any close contacts at SoundField to which they can ask
these questions?

When I asked them at the AES about this, Mr Bacon told me that it was not
an Ambisonic decode but two stereo decodes. However, Dave Malham disagreed
with this in the list when I mentioned it, so maybe he could comment.
I've just moved offices so I can't lay my hands on the data sheet right
now, but I seem to recall that you can set the stage widths and stuff, so I
don't think your subject line is exactly warranted.
In any event, speaker positions for 5.1 as a whole (ie the standard to
which G-format would best decode) are not going to be decided by a small
manufacturer: it's more likely to be people like Dolby and THX. Although we
can put our views about, most likely we will be following industry
standards, not setting them.
--Richard Elen

[DG Malham]

I haven't access to a MkV to check, but the MKIII produces exactly the
same level from all four outputs. It certainly sounds like a fault
condition. The question is, is it in the test signal circuitry or in the
output buffer amp? It is, in either case, unlikely to be on a variable
control - in these days of 1% resistors being the norm rather than a very,
very expensive option, it is normal (and much better in terms of long-term
drift) to set levels with fixed resistors wherever possible. It might pay
to analyise the signals coming out, for instance by looking for excessive
out-of-phase signals on the rear channels when decoding a prominent
frontal source (the piano you recorded would probably work fine). If that
proves that the signals from the capsules themselves are producing correct
B format at the output, then it is only the test signal which is wrong and
not the output buffer - I would be inclined to live with that (until such
time as you can get it sorted out without causing too much hassle to
yourself) by just making careful notes on the tape as to the levels of the
test tones so as to avoid confusion when working with the tape in future.

Incidentally, the 3dB difference is (in the MKIII and, as far as I am
aware, all other Soundfields) in the A-B matrix where the mic capsule
signals are converted to B Format.

Dave

/**************************************************************************/
/* Dave Malham "http://www.york.ac.uk/depts/music/dgm.htm" */
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/* Department of Music "http://www.york.ac.uk/depts/music/welcome.htm" */
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/* "http://www.york.ac.uk/inst/mustech/3d_audio/ambison.htm" */
/**************************************************************************/

Post by farina
Yesterday I recorded a piano concert at the Teatro Comunale of Ferrara with
my Soundfield MKV microphone and my new multi-channel DAT (SONY PC-208),
employing the latter in the 4-channels mode.
At the beginning, I recorded 30s of the special test signal generated from
the Soundfield control unit: it is an 1 kHz tone, which is steady on channel
W, and intermittent on the X,Y and Z.
Today I have transferred the recording on my PC (through the Layla sound
board), and I discovered that the reference signals have different
amplitudes: the W signal is 2.2 dB lower than X, Y and Z. I have checked the
DAT, but I discovered that this level mismatch comes from the Soundfield
itself.
Now, the question is: what should be the output levels of the reference
signals? Does the W channels have to be exactly 3 dB lower than the other 3,
or does it have to be at the same level? It depends on the fact that the 3
dB attenuation is before or after the electronic signal generator inside the
Soundfield... The manual says that the reference signal should be 0 dBm on
all the 4 channels...
Is it possible to re-calibrate the output levels of the Soundfield
microphone (without sending it back to the UK)?
Can anyone help me?
Bye!
Angelo Farina
Dipartimento di Ingegneria Industriale
Universita' di Parma
Via delle Scienze - 43100 PARMA (Italy)
HTTP://pcfarina.eng.unipr.it
tel. [phone] - fax [phone]
-----Original Message-----
Date: Friday, November 20, 1998 23:46
Subject: Re: sursound: G-Format (with HEIGHT) de factor standard
alreadyset??!!

SoundField has introduced its 5.1 microphone system. This allows recording
and broadcast engineers to facilitate a complete 5.1 mix from a single
multiple element microphone...
I wonder...
1) What angular dimensions are these derived speaker feed signals at?
and
2) How is the W signal incorporated?
Does anyone have any close contacts at SoundField to which they can ask
these questions?

When I asked them at the AES about this, Mr Bacon told me that it was not
an Ambisonic decode but two stereo decodes. However, Dave Malham disagreed
with this in the list when I mentioned it, so maybe he could comment.
I've just moved offices so I can't lay my hands on the data sheet right
now, but I seem to recall that you can set the stage widths and stuff, so I
don't think your subject line is exactly warranted.
In any event, speaker positions for 5.1 as a whole (ie the standard to
which G-format would best decode) are not going to be decided by a small
manufacturer: it's more likely to be people like Dolby and THX. Although we
can put our views about, most likely we will be following industry
standards, not setting them.
--Richard Elen

[Mark Decker]

Hi Angelo,
I have just been down to the studio and fired up our Mk IV Soundfield,
looking at the bargraphs on the front of the control unit, all 4 signals are
reading the same level. Checking on a BBC PPM, not the most accurate for
absolute levels, but O.K. for checking relative levels, all 4 signals read
PPM 4 (i.e. BBC zero level).
Hope that is of some use.
Mark Decker

Post by farina
-----Original Message-----
Sent: Thursday, November 26, 1998 8:58 PM
Subject: sursound: Level alignment of Soundfield microphones
Yesterday I recorded a piano concert at the Teatro Comunale of Ferrara
with
my Soundfield MKV microphone and my new multi-channel DAT (SONY PC-208),
employing the latter in the 4-channels mode.
At the beginning, I recorded 30s of the special test signal generated from
the Soundfield control unit: it is an 1 kHz tone, which is steady on
channel
W, and intermittent on the X,Y and Z.
Today I have transferred the recording on my PC (through the Layla sound
board), and I discovered that the reference signals have different
amplitudes: the W signal is 2.2 dB lower than X, Y and Z. I have checked
the
DAT, but I discovered that this level mismatch comes from the Soundfield
itself.
Now, the question is: what should be the output levels of the reference
signals? Does the W channels have to be exactly 3 dB lower than the other
3,
or does it have to be at the same level? It depends on the fact that the 3
dB attenuation is before or after the electronic signal generator inside
the
Soundfield... The manual says that the reference signal should be 0 dBm on
all the 4 channels...
Is it possible to re-calibrate the output levels of the Soundfield
microphone (without sending it back to the UK)?
Can anyone help me?
Bye!
Angelo Farina
Dipartimento di Ingegneria Industriale
Universita' di Parma
Via delle Scienze - 43100 PARMA (Italy)
HTTP://pcfarina.eng.unipr.it
tel. [phone] - fax [phone]
-----Original Message-----
Date: Friday, November 20, 1998 23:46
Subject: Re: sursound: G-Format (with HEIGHT) de factor standard
alreadyset??!!

SoundField has introduced its 5.1 microphone system. This allows

recording

and broadcast engineers to facilitate a complete 5.1 mix from a single
multiple element microphone...
I wonder...
1) What angular dimensions are these derived speaker feed signals at?
and
2) How is the W signal incorporated?
Does anyone have any close contacts at SoundField to which they can ask
these questions?

When I asked them at the AES about this, Mr Bacon told me that it was not
an Ambisonic decode but two stereo decodes. However, Dave Malham

disagreed

with this in the list when I mentioned it, so maybe he could comment.
I've just moved offices so I can't lay my hands on the data sheet right
now, but I seem to recall that you can set the stage widths and stuff, so

I

don't think your subject line is exactly warranted.
In any event, speaker positions for 5.1 as a whole (ie the standard to
which G-format would best decode) are not going to be decided by a small
manufacturer: it's more likely to be people like Dolby and THX. Although

we

can put our views about, most likely we will be following industry
standards, not setting them.
--Richard Elen

[Jeff Silberman-SurroundWorks(tm)]

I send my St-250 to Soundfield once per year for calibration lest I waste
my time recording in B-format. Invariably, Soundfield finds the unit out
of spec each time. Slight imbalances may not be noticeable unless one is
very critical in monitoring.

A while ago, I posted to this list that a fellow St-250 owner had all four
of his capsules replaced at Soundfield's suggestion. His was an ST-250
manafactured under the auspices of AMS. Soundfield's Richard Bacon
told me that only 1/4 of the capsules made during that time are "good".
My St-250 - also an AMS manafactured one- is one of the lucky ones
apparently. This gentleman also needed fixes to his A-B matrix box ...

Soundfield does not feel that my yearly check-up is ill-advised.
Of course, YMMV.

Dave Malham wrote....

Subject: Re: sursound: Level alignment of Soundfield microphones
I haven't access to a MkV to check, but the MKIII produces exactly the
same level from all four outputs. It certainly sounds like a fault
condition. The question is, is it in the test signal circuitry or in the
output buffer amp?

When one buys a porche (and pays a porche price) one expects that it
has been checked before leaving the factory.
My experience with the purchase of an ST250 last year was that it couldn't
possibly have been checked properly, necessitating replacement of the
complete processing unit.
I wonder how many users of these beautiful microphones have never checked
the accuracy of them. I suspect most. Like I said, when you buy a porche.....
let the buyer beware.....
D.
--
___________________________________________________
Head, Australian Centre for the Arts and Technology
Australian National University
President, Australasian Computer Music Association
GPO Box 804 Canberra Australia 2601
'phone: [phone] Fax: [phone]
http://online.anu.edu.au/ITA/ACAT/drw/
___________________________________________________

[David Worrall]

On Nov 27, 9:54am, DG Malham wrote:
Dave Malham wrote....

Subject: Re: sursound: Level alignment of Soundfield microphones
I haven't access to a MkV to check, but the MKIII produces exactly the
same level from all four outputs. It certainly sounds like a fault
condition. The question is, is it in the test signal circuitry or in the
output buffer amp?

When one buys a porche (and pays a porche price) one expects that it
has been checked before leaving the factory.

My experience with the purchase of an ST250 last year was that it couldn't
possibly have been checked properly, necessitating replacement of the
complete processing unit.

I wonder how many users of these beautiful microphones have never checked
the accuracy of them. I suspect most. Like I said, when you buy a porche.....

let the buyer beware.....

D.
--
___________________________________________________
Head, Australian Centre for the Arts and Technology
Australian National University
President, Australasian Computer Music Association

GPO Box 804 Canberra Australia 2601
'phone: [phone] Fax: [phone]
email: ***@anu.edu.au
http://online.anu.edu.au/ITA/ACAT/drw/
___________________________________________________