Re: [Sursound] More Capsules - More Self-Noise Or Less?

[Jack Reynolds]

I could refer you back to Prof Angelo Farina’s input on the subject.

He confirmed the 3dB increase in noise per order. 

Just out of interest - who designed your encoder?

The increase in signal level was when you add two back to back cardioids was 
also confirmed by someone whose opinion I suspect you would trust even more 
than Angelo. 

Perhaps Prof Farina will chime in with his opinion.

The link you posted doesn’t lead anywhere useful by the way, it just takes you 
to a particular Facebook group. 

J
Sent from my iPhone

> On 9 Nov 2023, at 12:56, lenmoskow...@optonline.net wrote:
> 
> 
>> You get a 3dB increase of noise per order of ambisonics, which is why 
>> eight-capsule hybrid second order microphones can actually sound noisier 
>> than first order microphones.
>  
> That's true only if you don't know how to properly design an HOA encoder.
>  
>  
> Len Moskowitz (mosko...@core-sound.com)
> Core Sound LLC
> www.core-sound.com 
>  
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[Jack Reynolds]

The measurements will be the source of truth. 

J

Sent from my iPhone

> On 9 Nov 2023, at 12:56, lenmoskow...@optonline.net wrote:
> 
> 
>> You get a 3dB increase of noise per order of ambisonics, which is why 
>> eight-capsule hybrid second order microphones can actually sound noisier 
>> than first order microphones.
>  
> That's true only if you don't know how to properly design an HOA encoder.
>  
>  
> Len Moskowitz (mosko...@core-sound.com)
> Core Sound LLC
> www.core-sound.com 
>  
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[lenmoskowitz]

You get a 3dB increase of noise per order of ambisonics, which is why 
eight-capsule hybrid second order microphones can actually sound 
noisier than first order microphones.

 
That's true only if you don't know how to properly design an HOA 
encoder.

 
 
Len Moskowitz (mosko...@core-sound.com)
Core Sound LLC
www.core-sound.com 
 
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[lenmoskowitz]

You'll have to argue with Prof. Angelo Farina. Frankly, between the two 
of you, I know whom to trust.

 
https://www.facebook.com/groups/Ambisonics.VR.360.Audio/?multi_permalinks=5265393360254911¬if_id=1666553911378133 


 
Angelo Farina wrote:
I can answer about the microphones. What matters is their number, not 
their arrangement. The noise floor of each 
Ambisonics signal is lowered by 3 dB for each doubling of the number of 
microphones. So, if a single capsule has 
a noise floor of 20 dB(A), when you use 4 capsules the W channel will 
have a noise floor reduced by 6 dB, 
14 dB(A). If you use 8 capsules, the W channel will have a further 
reduction of 3 dB, hence 11 dB(A). 
If you use 32 capsules (Eigenmike) the noise floor will be down other 6 
dB, at 5 dB(A).

 
---
One of the standard mic theory texts also confirms this.
 
Len Moskowitz (mosko...@core-sound.com)
Core Sound LLC
www.core-sound.com 
Home of OctoMic and TetraMic
 
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[Jack Reynolds]

The other thing to add to this point is the 3dB (not 9dB) improvement in signal 
to noise ratio ONLY APPLIES TO THE W CHANNEL, which ignores the noise on the 
other eight channels of your B-Format. 

You get a 3dB increase of noise per order of ambisonics, which is why 
eight-capsule hybrid second order microphones can actually sound noisier than 
first order microphones. 

Hence the various settings in A-Format to B-Format encoders that essentially 
bring down the level of the second order components to reduce the hiss, at the 
expense of a certain amount of spatial resolution. 

Cheers

Jack

Sent from my iPhone

> On 9 Nov 2023, at 08:51, Jack Reynolds  wrote:
> 
> Hi Len,
> 
> As we’ve discussed before…
> 
> This simply isn’t true.
> 
> If you add two omnidirectional microphones together you get a 6dB increase in 
> peak audio signal (voltage) but only a 3dB increase in noise because noise is 
> an average power. P=I^2*R and V=IR. The square makes the difference. 
> 
> If you double the number of capsules twice, i.e. adding eight omnis, you get 
> a 9dB increase in noise (3*3) and a 24dB increase in peak signal (3*6). 
> 
> A 15dB increase in signal to noise ratio  (SNR, the difference between the 
> peak signal and the noise power, expressed in decibels).
> 
> Adding eight cardioids together to create a single omni W channel for 
> ambisonic use is not the same thing at all. 
> 
> Cardioids are made up of an omnidirectional, pressure component and a 
> velocity, figure-of-eight component.
> 
> If you add two cardioids, pointing in opposite directions, the figure of 
> eight components cancel out, leaving just the omnidirectional components. 
> 
> The omni component is only half of the energy of the cardioid microphone, so 
> you only get half the peak signal benefit when adding cardioids arranged in 
> A-Format to produce a B-Format W channel. 
> 
> Adding eight cardioids in A-Format arrangement will give you 9dB more noise, 
> but only a 12dB (24/2) increase in peak level. An increase in signal to noise 
> ratio of 3dB. Not 9dB.
> 
> So if you are expecting a 9dB increase in SNR and your published 15dBA SNR, 
> which is equivalent to 79dB signal to noise ratio, is based on that 
> assumption, those numbers can’t possibly be accurate. 
> 
> If your mic has eight capsules and you claim you are getting a 9dB SNR 
> benefit from adding the capsules that would imply 70dB SNR per capsule 
> (79-9). 
> 
> I suspect that number should actually be more like 21dBA or 73dB SNR for the 
> W omni channel and 70dB SNR per single capsule, since you only get a 3dB SNR 
> benefit when adding eight. 
> 
> We will confirm these numbers by measuring a single Tetramic capsule on axis 
> with a known SPL white noise signal and subsequently comparing the single 
> capsule numbers to the W channel SNR.
> 
> I’m sorry to have to point these things out. I just want transparency in our 
> industry and any misleading claims or doubts cast on our mic comparison study 
> must be addressed. 
> 
> Cheers
> 
> Jack
> 
> Sent from my iPhone
> 
>> On 9 Nov 2023, at 01:37, lenmoskow...@optonline.net wrote:
>> Do Many Small Capsules Mean More Self-Noise Or Less? Less!
>> 
>> 
>> As we've discussed before, the more capsules an array microphone has, the 
>> lower its self-noise. That's because as you double the number of capsules, 
>> the combined output voltage goes up 6 dB, but the self-noise only goes up 3 
>> dB.
>> 
>> The noise increases only 3 dB  because it's uncorrelated across capsules. So 
>> each time you double the number of capsules, self-noise drops 3 dB. 
>> OctoMic's combined eight capsules have 9 dB lower self-noise than a single 
>> capsule.
>> 
>> That results in a low self-noise specification.  We specify it 
>> conservatively as 15 dBA. That's the same as DPA's wonderful 4003, or only 1 
>> dB more than Schoeps' Mk 4.
>> 
>> 
>> 
>> Len Moskowitz (mosko...@core-sound.com)
>> Core Sound LLC
>> www.core-sound.com
>> Home of OctoMic and TetraMic
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[Jack Reynolds]

Hi Len,

As we’ve discussed before…

This simply isn’t true.

If you add two omnidirectional microphones together you get a 6dB increase in 
peak audio signal (voltage) but only a 3dB increase in noise because noise is 
an average power. P=I^2*R and V=IR. The square makes the difference. 

If you double the number of capsules twice, i.e. adding eight omnis, you get a 
9dB increase in noise (3*3) and a 24dB increase in peak signal (3*6). 

A 15dB increase in signal to noise ratio  (SNR, the difference between the peak 
signal and the noise power, expressed in decibels).

Adding eight cardioids together to create a single omni W channel for ambisonic 
use is not the same thing at all. 

Cardioids are made up of an omnidirectional, pressure component and a velocity, 
figure-of-eight component.

If you add two cardioids, pointing in opposite directions, the figure of eight 
components cancel out, leaving just the omnidirectional components. 

The omni component is only half of the energy of the cardioid microphone, so 
you only get half the peak signal benefit when adding cardioids arranged in 
A-Format to produce a B-Format W channel. 

Adding eight cardioids in A-Format arrangement will give you 9dB more noise, 
but only a 12dB (24/2) increase in peak level. An increase in signal to noise 
ratio of 3dB. Not 9dB.

So if you are expecting a 9dB increase in SNR and your published 15dBA SNR, 
which is equivalent to 79dB signal to noise ratio, is based on that assumption, 
those numbers can’t possibly be accurate. 

If your mic has eight capsules and you claim you are getting a 9dB SNR benefit 
from adding the capsules that would imply 70dB SNR per capsule (79-9). 

I suspect that number should actually be more like 21dBA or 73dB SNR for the W 
omni channel and 70dB SNR per single capsule, since you only get a 3dB SNR 
benefit when adding eight. 

We will confirm these numbers by measuring a single Tetramic capsule on axis 
with a known SPL white noise signal and subsequently comparing the single 
capsule numbers to the W channel SNR.

I’m sorry to have to point these things out. I just want transparency in our 
industry and any misleading claims or doubts cast on our mic comparison study 
must be addressed. 

Cheers

Jack

Sent from my iPhone

> On 9 Nov 2023, at 01:37, lenmoskow...@optonline.net wrote:
> Do Many Small Capsules Mean More Self-Noise Or Less? Less!
> 
> 
> As we've discussed before, the more capsules an array microphone has, the 
> lower its self-noise. That's because as you double the number of capsules, 
> the combined output voltage goes up 6 dB, but the self-noise only goes up 3 
> dB.
> 
> The noise increases only 3 dB  because it's uncorrelated across capsules. So 
> each time you double the number of capsules, self-noise drops 3 dB. OctoMic's 
> combined eight capsules have 9 dB lower self-noise than a single capsule.
> 
> That results in a low self-noise specification.  We specify it conservatively 
> as 15 dBA. That's the same as DPA's wonderful 4003, or only 1 dB more than 
> Schoeps' Mk 4.
> 
> 
> 
> Len Moskowitz (mosko...@core-sound.com)
> Core Sound LLC
> www.core-sound.com
> Home of OctoMic and TetraMic
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Re: [Sursound] More Capsules - More Self-Noise Or Less?

[Rudy Chalupa]

 But isn't that only true if all the capsules are picking up the full signal? 
In the case of an Ambisonic mike, where the directional capsules are pointed in 
various directions, you won't get the full advantage.
Cordially,
Rudy ChalupaPleiades Audio + Electronics
On Wednesday, November 8, 2023 at 08:37:52 PM EST, 
lenmoskow...@optonline.net  wrote:  
 
 Do Many Small Capsules Mean More Self-Noise Or Less? Less!


As we've discussed before, the more capsules an array microphone has, 
the lower its self-noise. That's because as you double the number of 
capsules, the combined output voltage goes up 6 dB, but the self-noise 
only goes up 3 dB.

The noise increases only 3 dB  because it's uncorrelated across 
capsules. So each time you double the number of capsules, self-noise 
drops 3 dB. OctoMic's combined eight capsules have 9 dB lower self-noise 
than a single capsule.

That results in a low self-noise specification.  We specify it 
conservatively as 15 dBA. That's the same as DPA's wonderful 4003, or 
only 1 dB more than Schoeps' Mk 4.



Len Moskowitz (mosko...@core-sound.com)
Core Sound LLC
www.core-sound.com
Home of OctoMic and TetraMic
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[Sursound] More Capsules - More Self-Noise Or Less?

[lenmoskowitz]

Do Many Small Capsules Mean More Self-Noise Or Less? Less!


As we've discussed before, the more capsules an array microphone has, 
the lower its self-noise. That's because as you double the number of 
capsules, the combined output voltage goes up 6 dB, but the self-noise 
only goes up 3 dB.


The noise increases only 3 dB  because it's uncorrelated across 
capsules. So each time you double the number of capsules, self-noise 
drops 3 dB. OctoMic's combined eight capsules have 9 dB lower self-noise 
than a single capsule.


That results in a low self-noise specification.  We specify it 
conservatively as 15 dBA. That's the same as DPA's wonderful 4003, or 
only 1 dB more than Schoeps' Mk 4.




Len Moskowitz (mosko...@core-sound.com)
Core Sound LLC
www.core-sound.com
Home of OctoMic and TetraMic
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