[Sursound] Sursound Digest, Vol 121, Issue 13

Florian Grond

2018-08-28 13:07:52 UTC

Hi everyone,

Regarding the question of which mems the ZM-1 uses, here is some detailed
info I just found:
https://www.infineon.com/cms/en/about-infineon/press/market-news/2018/INFPMM201808-078.html

Best,

Florian

www.grond.at

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important.
1. MEMS SNR Specifications (Ralph Jones)
2. Re: MEMS SNR Specifications (Paul Hodges)
3. Re: MEMS SNR Specifications (Jack Reynolds)
4. Re: MEMS SNR Specifications (Bo-Erik Sandholm)
5. Re: MEMS SNR Specifications (Chris Woolf)
6. Re: MEMS SNR Specifications (Fons Adriaensen)
----------------------------------------------------------------------
Message: 1
Date: Fri, 17 Aug 2018 14:55:36 -0700
Subject: [Sursound] MEMS SNR Specifications
Content-Type: text/plain; charset=utf-8
There?s been some interesting discussion here about
Micro-ElectroMechanical Systems (MEMS) microphones for ambisonic mic
arrays. These devices seem to offer some compelling qualities (particularly
small size and low cost) but their signal-to-noise spec is 65 dBA. Some
folks posting here have seemed to suggest that this level of noise might
possibly be acceptable.
IMHO, based on decades of experience, a microphone with a signal-to-noise
ratio of 65 dBA is useless for professional recording. That's in the SNR
range typical of consumer cassette tape machines or analog AM radio.
For comparison, consider that professional large-diaphragm condenser mics
achieve 120-130 dB SNR. The Sennheiser Ambeo has an SNR of about 110 dB.
Portable digital audio recorders and popular audio interfaces make about
100 dB, and Red Book CDs 98 dB. Even vinyl records are about 6 dB quieter
than MEMS mic elements.
Put a MEMS mic at the input of a digital recorder and you?re wasting 35 dB
of dynamic range (not to mention the case of using several of them in an
ambisonic array). That?s huge. A symphony orchestra playing at mezzoforte
or louder may mask the noise if the mic is reasonably close to the stage,
but forget trying to record softer passages. Recordists trying to capture
natural ambiences will be sorely disappointed; a lot of what they?re trying
to record will simply disappear into the noise floor. You might get away
with using it for non-critical functions like background crowd noise for
telecasts of sporting events, but that?s about it.
MEMS mics appear to me to have been developed for applications that
require very small size, physical ruggedness, reasonable frequency response
and low cost, but can tolerate a high noise floor. There are lots of such
use cases, but professional audio is not one of them. If we wish to advance
the art of ambisonic recording and reproduction, we cannot compromise basic
performance specifications for the sake of a trendy idea.
Ralph Jones
------------------------------
Message: 2
Date: Fri, 17 Aug 2018 23:56:21 +0100
Subject: Re: [Sursound] MEMS SNR Specifications
Content-Type: text/plain; charset=us-ascii

Some folks posting here have seemed to suggest that this level of
noise might possibly be acceptable.

Well, firstly we don't know the actual specification of the devices
used by Zylia. And secondly, using an array of nineteen to generate an
output gives the possibility of significant improvement, because the
sound source signals are correlated and the noise is uncorrelated.
How this holds up in practice at higher orders and higher frequencies I
will attempt to judge when I get my hands on the ZM-1 rather than just
predicting failure in advance (which is not consistent with the reviews
I've seen heard and read).
Paul
--
Paul Hodges
------------------------------
Message: 3
Date: Sat, 18 Aug 2018 00:37:22 +0100
Subject: Re: [Sursound] MEMS SNR Specifications
Content-Type: text/plain; charset=us-ascii
Are you sure the Ambeo has 110dB SNR?
Sent from my iPhone

Some folks posting here have seemed to suggest that this level of
noise might possibly be acceptable.

Well, firstly we don't know the actual specification of the devices
used by Zylia. And secondly, using an array of nineteen to generate an
output gives the possibility of significant improvement, because the
sound source signals are correlated and the noise is uncorrelated.
How this holds up in practice at higher orders and higher frequencies I
will attempt to judge when I get my hands on the ZM-1 rather than just
predicting failure in advance (which is not consistent with the reviews
I've seen heard and read).
Paul
--
Paul Hodges
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------------------------------
Message: 4
Date: Sat, 18 Aug 2018 09:41:13 +0200
Subject: Re: [Sursound] MEMS SNR Specifications
<CAEAiL24g=oFicUeY4cjyxxGebA7YPnP3ZHSmRN9Hp3gFoW+==
Content-Type: text/plain; charset="utf-8"
According to the document linked to below that relates self noise values to
real world applications 110 SNR cannot be related to the commonly used
reference sound level.
110 dBA SNR would be 16 dB below absolute quiet.
If the value 70dBA that I found for the infineon dual membrane MEMS mic is
related to 1 Pascal, then it's self noise is around 24 dB which is not
strictly studio quality.
But not really horrible.
If it is related to max 10% distortion which is at 135 dBA thats not a
realistic comparison value as the result is a self noise of 65 dBA.
That would be a noise source not a microphone :-) !
So a bit of apples and oranges comparison is going on ??
http://www.neumann.com/homestudio/en/what-is-self-noise-or-equivalent-noise-level
SIGNAL-TO-NOISE RATIO
Another way to document the noise performance is to specify the
signal-to-noise ratio. But relative to what signal? The reference sound
pressure level for noise measurements is 94 dB (which equals a sound
Signal-to-noise (db-A) = 94 dB ? self-noise (dB-A)
The actual signal-to-noise ratio in use, of course, depends on the sound
pressure level of your sound source.
Bo-Erik

Are you sure the Ambeo has 110dB SNR?
Sent from my iPhone

Some folks posting here have seemed to suggest that this level of
noise might possibly be acceptable.

Well, firstly we don't know the actual specification of the devices
used by Zylia. And secondly, using an array of nineteen to generate an
output gives the possibility of significant improvement, because the
sound source signals are correlated and the noise is uncorrelated.
How this holds up in practice at higher orders and higher frequencies I
will attempt to judge when I get my hands on the ZM-1 rather than just
predicting failure in advance (which is not consistent with the reviews
I've seen heard and read).
Paul
--
Paul Hodges
_______________________________________________
Sursound mailing list
https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe

here,

edit account or options, view archives and so on.
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Message: 5
Date: Sat, 18 Aug 2018 09:56:57 +0100
Subject: Re: [Sursound] MEMS SNR Specifications
Content-Type: text/plain; charset=utf-8; format=flowed
I think there is indeed some confusion in this discussion between the
signal-to-noise ratio of these mics, and dynamic range.
The first is conventionally related to 1Pa/94dB SPL, and one then needs
to add in a Max SPL figure to get the dynamic range.
We need both bits of information to understand the practicality of any mic.
A noise floor of 24dBA (related to 1Pa) is about par for a small
personal electret mic. A dynamic range of >115dB is what one would wish
for in decent professional mics - that would be a noise floor of 15dBA
and a max SPL of >130dB (with a distortion figure of 3 or 5%).
Chris Woolf (ex editor of Microphone Data)

According to the document linked to below that relates self noise values

real world applications 110 SNR cannot be related to the commonly used
reference sound level.
110 dBA SNR would be 16 dB below absolute quiet.
If the value 70dBA that I found for the infineon dual membrane MEMS mic

related to 1 Pascal, then it's self noise is around 24 dB which is not
strictly studio quality.
But not really horrible.
If it is related to max 10% distortion which is at 135 dBA thats not a
realistic comparison value as the result is a self noise of 65 dBA.
That would be a noise source not a microphone :-) !
So a bit of apples and oranges comparison is going on ??

http://www.neumann.com/homestudio/en/what-is-self-noise-or-equivalent-noise-level

SIGNAL-TO-NOISE RATIO
Another way to document the noise performance is to specify the
signal-to-noise ratio. But relative to what signal? The reference sound
pressure level for noise measurements is 94 dB (which equals a sound
Signal-to-noise (db-A) = 94 dB ? self-noise (dB-A)
The actual signal-to-noise ratio in use, of course, depends on the sound
pressure level of your sound source.
Bo-Erik

Are you sure the Ambeo has 110dB SNR?
Sent from my iPhone

Some folks posting here have seemed to suggest that this level of
noise might possibly be acceptable.

Well, firstly we don't know the actual specification of the devices
used by Zylia. And secondly, using an array of nineteen to generate an
output gives the possibility of significant improvement, because the
sound source signals are correlated and the noise is uncorrelated.
How this holds up in practice at higher orders and higher frequencies I
will attempt to judge when I get my hands on the ZM-1 rather than just
predicting failure in advance (which is not consistent with the reviews
I've seen heard and read).
Paul
--
Paul Hodges
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https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe

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Message: 6
Date: Sat, 18 Aug 2018 11:52:59 +0200
Subject: Re: [Sursound] MEMS SNR Specifications
Content-Type: text/plain; charset=us-ascii

According to the document linked to below that relates self noise values

real world applications 110 SNR cannot be related to the commonly used
reference sound level.
110 dBA SNR would be 16 dB below absolute quiet.

Maybe possible with an unexistium membrane and left twisting electrons ...
:-)

If the value 70dBA that I found for the infineon dual membrane MEMS mic

related to 1 Pascal, then it's self noise is around 24 dB which is not
strictly studio quality. But not really horrible.

It's the self noise figure which matters in the end. It simply means
that if you record a sound with an SPL of say 60 dB (at the mic), the
S/N ratio would be 60 - 24 = 36 dB. Using a 'pro' mic with a self
noise of 10 dB the S/N ratio would be 50 dB. In both cases assuming
the preamp doesn't add a significant amount of noise.
Noise of 'virtual mics' (or ambisonice components) synthesised from
multiple capsules is not so simple.
If S_i is the signal from the i-th capsule then the beam signal is
of the form
S_beam = sum (a_i * S_i) i = 1..B
where the a_i are complex gains depending of frequency. Now if the
a_i are scaled such that the on-axis sensitivity of the beam is the
same as that for a single capsule, then the noise power in the beam
N_beam = sum (a_i ^ 2)
For an 'omni' pattern this typically results in a significant
improvement, up to 3dB * log2 (N) in the best case (ommi
capsules at low and medium frequencies).
For directive patterns, almost anything can happen depending
on if the capsules are omni or directional, if they are in
free space or on a solid body, and the order of the pattern.
The actual noise will not be white which means that traditional
noise figures (e.g. A-weighted) become more or less useless.
Typically you may see some improvement over the single capsule
noise level in some small frequency region, and more noise
in other frequency bands.
For some examples, get hold of the original Eigenmic manual
which shows noise performance as a function of frequency
for each of the available patterns. That's the only example
I know of a manufacturer documenting this, most (including
Zylia) will hide the truth in lots of blabla.
Ciao,
--
FA
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