Question about microphone self-noise measurement

[KenElevenShadows]

First off, I am not super-knowledgeable about the precise method for measuring self-noise in a microphone.

 

Usually, self-noise is given in dB-A. The “A” stands for A-weighting, which is a method to simulate human perception. When I see manufacturers giving self-noise figures in this manner, I typically see something like, say, "Self-noise of 10 dB-A." And this is usually considered pretty good since the ambient noise of a room is often going to be louder than this anyway. 

 

I came across a video microphone. The manufacturer claims  that it has self-noise of -76dBA. How are they arriving at this figure, and what does it mean? Thanks!

[KuruPrionz]

Without precision electronics for tools, it's difficult to get accurate measurements. 

Vendors use various strategies to skew those numbers in their favor, the whole "600 watts peak, 150 watts RMS" thing for example. 

 

I just plug a mic in, set the volume in a usable range and listen on headphones. Then I unplug the mic from the system and see if the noise changes. Then I unplug the cord and check again. Most modern mics are pretty quiet, certainly usable. 

 

Wouldn't "-76dBA" mean that a microphone's noise level is quieter than absolute silence? 😜

[KenElevenShadows]

Haha! Sure, it's actually sucking in the silence!

 

Just for giggles, I asked my old friend, ChatGPT, for answers:

 

"When a microphone is in operation, it produces some inherent noise, which is referred to as self-noise. The self-noise level of a microphone is typically measured in dB(A) or dB SPL, which stands for decibels of sound pressure level.

 

In the case of a microphone rated at having self-noise of -76dBa, this means that the microphone's self-noise level is 76 dB below the standard reference level for sound pressure (i.e., 0 dB SPL). In other words, the microphone produces a very low level of noise, which is generally considered to be very good.

 

It is indeed possible for a microphone to have a self-noise level of -76 dBa, and some high-end microphones do have this level of noise performance. However, it's worth noting that the self-noise level of a microphone is only one factor to consider when choosing a microphone for a specific application, and other factors such as frequency response, polar pattern, and sensitivity may also be important."

 

Now, this isn't necessarily ChatGPT's strong suit. It does other things well, such as summarizing or re-phrasing text, creating ideas, creating outlines, creating generic explanations or marketing plans, and other things. 

 

But just simply finding answers? It's okay. It gets a lot of information wrong. 

 

Will this be correct?

[KuruPrionz]

22 minutes ago, KenElevenShadows said:

Haha! Sure, it's actually sucking in the silence!

 

Just for giggles, I asked my old friend, ChatGPT, for answers:

 

"When a microphone is in operation, it produces some inherent noise, which is referred to as self-noise. The self-noise level of a microphone is typically measured in dB(A) or dB SPL, which stands for decibels of sound pressure level.

 

In the case of a microphone rated at having self-noise of -76dBa, this means that the microphone's self-noise level is 76 dB below the standard reference level for sound pressure (i.e., 0 dB SPL). In other words, the microphone produces a very low level of noise, which is generally considered to be very good.

 

It is indeed possible for a microphone to have a self-noise level of -76 dBa, and some high-end microphones do have this level of noise performance. However, it's worth noting that the self-noise level of a microphone is only one factor to consider when choosing a microphone for a specific application, and other factors such as frequency response, polar pattern, and sensitivity may also be important."

 

Now, this isn't necessarily ChatGPT's strong suit. It does other things well, such as summarizing or re-phrasing text, creating ideas, creating outlines, creating generic explanations or marketing plans, and other things. 

 

But just simply finding answers? It's okay. It gets a lot of information wrong. 

 

Will this be correct?

ChatGPT got the most important part right. The "other factors" are a big deal. In my current location, there is a bit of background noise. Some of it is on schedule - I-5 freeway noise is loudest during morning and late afternoon when people come and go to work. Some of it is random - 33 unit complex and parking nearby. 

I've found time and again that in this situation a cardioid dynamic mic will pick up far less background noise than a super or hyper cardioid, which both have a small area of pickup on the backside of the mic. It will also pickup less background noise than a cardioid condenser mic or any omni or figure of 8 mic. I can't use a ribbon mic here, just for one - they are almost all figure of 8 pattern. 

 

The background noise is always the issue here, most mics have low self noise. If your -76db mic picks up background noise you'll hear that on your recording. 

I've never tried using Izotope RX to remove that type of noise, will have to do that someday. 

[KenElevenShadows]

To me, Izotope RX is almost like magic. And I have an absurdly old version of it, and I can still take out most constant noises. I've even taken out door slams and other things before as well as hiss, 60-cycle hum, and that kind of thing.

[KuruPrionz]

53 minutes ago, KenElevenShadows said:

To me, Izotope RX is almost like magic. And I have an absurdly old version of it, and I can still take out most constant noises. I've even taken out door slams and other things before as well as hiss, 60-cycle hum, and that kind of thing.

I got version 7, 8 and now 9 and I've never used them. 

Mostly I record direct so there isn't much noise to deal with. I keep meaning to fire it up and see what it does. 

[Anderton]

8 hours ago, KenElevenShadows said:

I came across a video microphone. The manufacturer claims  that it has self-noise of -76dBA. How are they arriving at this figure, and what does it mean? Thanks!

 

Can't help you here, Ken. The only spec I truly understand with mics is: "Sounds good with my voice: Y/N"

[KenElevenShadows]

4 hours ago, KuruPrionz said:

I got version 7, 8 and now 9 and I've never used them. 

Mostly I record direct so there isn't much noise to deal with. I keep meaning to fire it up and see what it does. 

 

I think I have version 3, so I am waaaay behind.  

 

3 hours ago, Anderton said:

 

Can't help you here, Ken. The only spec I truly understand with mics is: "Sounds good with my voice: Y/N"

Isn't that the most important spec of all?

[KuruPrionz]

1 minute ago, KenElevenShadows said:

Isn't that the most important spec of all?

It is for me too. I have a couple that I really like for my voice and a few that are better for other things. 

I might swap around the ones that are good for other things but the vocal mics stay. 

[bill5]

12 hours ago, KenElevenShadows said:

I came across a video microphone. The manufacturer claims  that it has self-noise of -76dBA. How are they arriving at this figure, and what does it mean? Thanks!

The manufacturer apparently made a typo and meant 76, not -76. Basically you subtract that from 94 to get the signal-to-noise ratio that is commonly shown for mics (and where you'll see low numbers generally in the 5 to teens range), so in this case, 18, which is probably acceptable in most cases but no more. I would never buy a mic with a number higher than mid-teens if that, but that's because I have quiet sections of songs here and there where I really want that low noise spec to work for me vs making extra work for me.

 

And I would not trust ChatGPT for anything factual.  

[KenElevenShadows]

25 minutes ago, bill5 said:

The manufacturer apparently made a typo and meant 76, not -76. Basically you subtract that from 94 to get the signal-to-noise ratio that is commonly shown for mics (and where you'll see low numbers generally in the 5 to teens range), so in this case, 18, which is probably acceptable in most cases but no more. I would never buy a mic with a number higher than mid-teens if that, but that's because I have quiet sections of songs here and there where I really want that low noise spec to work for me vs making extra work for me.

 

And I would not trust ChatGPT for anything factual.  

 

That's why I mention that it gets a lot of information wrong and that it's not ChatGPT's strong suit. But thank you for pointing that out again.

 

I don't know that it's 76 db(A) either, as that seems absurdly loud. And this is why I initially asked the question.

[bill5]

Nah, as I mentioned, it's not great, but not terrible. Maybe you're confusing self-noise with signal-to-noise? 

[KenElevenShadows]

8 hours ago, bill5 said:

Nah, as I mentioned, it's not great, but not terrible. Maybe you're confusing self-noise with signal-to-noise? 

 

Nope, no confusion. 76dB(A) would be rather high for S/N for a microphone, to the point of where it would be unusable. You seem to be confused as to what I am asking and describing.

[Anderton]

I get confused about anythihg involving mic specs. Well, except for what kind of cable they need

 

FWIW this white paper by audio genius dude Dennis Bohn is the Gold Standard for a) understanding specifications, and b) understanding why most specifications are meaningless. As he says when discussing EIN, "This is a spec where test conditions are critical. It is very easy to deceive without them."

[bill5]

On 3/16/2023 at 9:33 PM, KenElevenShadows said:

 

Nope, no confusion. 76dB(A) would be rather high for S/N for a microphone, to the point of where it would be unusable. You seem to be confused as to what I am asking and describing.

Actually I read and answered too quickly and mixed up the two terms, which is probably what happened with the manufacturer. The "-76" was probably the signal-to-noise ratio (76, not -76), meaning the self-noise is 18. Which as I mentioned before isn't great and more than I'd care for, but not horrific. But as Anderton (by way of Bohn) pointed out, mic specs are of limited value at most (I think "meaningless" is pushing it a bit, but that's me), so it's largely much ado about nothing. 

[KuruPrionz]

20 minutes ago, bill5 said:

Actually I read and answered too quickly and mixed up the two terms, which is probably what happened with the manufacturer. The "-76" was probably the signal-to-noise ratio (76, not -76), meaning the self-noise is 18. Which as I mentioned before isn't great and more than I'd care for, but not horrific. But as Anderton (by way of Bohn) pointed out, mic specs are of limited value at most (I think "meaningless" is pushing it a bit, but that's me), so it's largely much ado about nothing. 

I haven't read Bohn's paper yet (I will) but II think the only way to make mic testing (such as it is) "real world" would be to establish a single microphone testing system that is used consistently.

Sadly, even that idea is deeply, hopelessly flawed. Proximity effect comes to mind as something that is not consistent and never will be - not even within the realm of a single company and a single type of microphone. 

For an example, both a Shure SM58 and a Shure KSM8 are cardioid dynamic microphones. If you get right up on an SM58 it gets very bass heavy and "boomy", a KSM8 does not do that. Yes, the designs are different but - how do you establish a consistent testing criteria for proximity effect? A Shure SM7b is also a cardioid dynamic mic but the grille is designed to keep your mouth farther away from the element, which reduces the proximity effect to a more usable degree. 

 

Omni directional mics exhibit very little proximity effect, you can destroy a ribbon mic by getting too close, plosives will stretch the ribbon and it won't shrink back. Most condenser mics sound much better if you get back a ways, plosives and sibilance are a problem with such a sensitive capsule. 

 

If there cannot reasonably be an optimum distance for running test frequencies, how can any further testing be consistent? If you test them all at 1 meter distance, you lose a huge part of why one person will prefer a particular microphone over another. 

 

In the end, we just have to try mics ourselves, find what we like and avoid what we don't. It's like food, friends and guitars, we are going to make different choices. 

[KuruPrionz]

The signal to noise ratio is directly related to proximity effect in that the closer a microphone is to a sound source (assuming the sound source does not create noise itself), the more signal you will get to noise. You can use a high pass filter to roll off the excess bass produced by proximity, some mic preamps have variable low pass filters and some have switches (which means it is going to roll off at a specific frequency whether you like it or not). 

 

With a vocalist, among the noise factors are breathing noise. A guitar amp can hum. Neither of those types of noise are generated by the microphone itself but they both can affect the signal to noise ratio in terms of the recording.

 

The length and quality of the cable can affect the signal to noise ratio as well. If a mic needs phantom power and the source is not true DC then that can cause a noise as well. LOTS of factors!!!

 

In the end, mic tests are not equivalent to real world use and never will be. If a mic works well for you, keep it. If it doesn't provide the results you are trying to achieve then continue the search. Not very scientific, I will admit. I will also admit that I've owned a good number of microphones and many are now somewhere else. Some of them I probably should have kept but in the end for a small personal studio 3 mics that work for what you are trying to do is probably enough. Which means I could still let some go at this point and I may very well do that. Somebody else's fun!!!! 😇

[Nathanael_I]

26 minutes ago, KuruPrionz said:

I haven't read Bohn's paper yet (I will) but II think the only way to make mic testing (such as it is) "real world" would be to establish a single microphone testing system that is used consistently.

 

https://www.audiotestkitchen.com/

 

They have put 300 microphones in the exact same rig with the exact same sources as scientifically controlled as is possible.  The results are quite useful.  You can audition 300 mics from your studio. 

[KuruPrionz]

1 minute ago, Nathanael_I said:

https://www.audiotestkitchen.com/

 

They have put 300 microphones in the exact same rig with the exact same sources as scientifically controlled as is possible.  The results are quite useful.  You can audition 300 mics from your studio. 

Cool, I'll take a look. Please read both of my posts, yes I am skeptical but I do have my reasons! 🙂

[KenElevenShadows]

I began this thread by saying that a video camera manufacturer had stated that the microphone had a self-noise of -76dBA. I questioned how that was even possible since I had only seen self-noise expressed in a positive manner since, well, the unit is making noise. And I certainly would never think that they would be able to achieve a self-noise of MINUS 76dBA.

 

So I contacted them and asked them to explain this.

 

Turns out that it was a misprint. Their self-noise is 20dBA. Now THAT sounds a lot more like one would expect.

 

Because of my email, they are now correcting the misprint.

 

[KenElevenShadows]

On 3/17/2023 at 10:02 PM, Nathanael_I said:

https://www.audiotestkitchen.com/

 

They have put 300 microphones in the exact same rig with the exact same sources as scientifically controlled as is possible.  The results are quite useful.  You can audition 300 mics from your studio. 

 

Seems extremely useful!

[KuruPrionz]

23 minutes ago, KenElevenShadows said:

 

Seems extremely useful!

They cover a lot of mics. They are probably adding more.

They don't cover my personal favorite condenser mics for bang for the buck (Microphone Parts), probably because they don't want to build them. But you can order them pre-built as well and they do cover the Roswell mics from the same vendor. I'm certain they've missed others, no dings. There are a LOT of microphone choices out there!!!

I did notice that they don't have the Blue Encore mics, the 300 is one I own and find useful. Huge bang for the buck on that one too.

 

It's a work in progress and a good one. I imagine it gets overwhelming. 

[Nathanael_I]

Audio Test Kitchen is wonderful for answering questions about how a given mic compares to something that you know. Whether that’s a 58 or a U47. And it is 100% internally consistent.  It’s a huge help if shopping for professionally priced microphones.  If shopping for a particular kind of mic, it allows easy comparisons of likely options. It isn’t universal, but it’s a huge service to the industry and has helped to improve the accuracy and consistency of mic specifications.  They are documenting what many manufacturers don’t publish.  It doesn’t answer all questions or have every mic, but it’s super useful.