New NIOSH Sound Level Meter App

168 comments on “New NIOSH Sound Level Meter App”

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Is there any app. available for android devices???

Thank you for the question, Asmaa. We discuss this issue on the frequently asked question section of our page https://www.cdc.gov/niosh/topics/noise/app.html. Basically, due to the fact that the Android marketplace is fragmented among many manufacturers with each having different hardware and software tools, it made it nearly impossible to verify the performance and accuracy of such an app on every model on the market today. If you’d like more information, see one of our first publications listed in the references section.

In my country the external microphone is not available at the same time i am trying to use the app with inbuilt microphone. Does it make much difference or just a few plus and minus with external and inbuilt microphone?

The main advantage to using an external microphone is the ability to calibrate the microphone before each measurement, not that it is more accurate than the internal microphone. The internal microphone are very capable and have good frequency response and dynamic range but they are hard to calibrate. The app comes with a nominal sensitivity for the internal microphone that allows the measurements to be within ± 2 dB(A).

Couldn’t you just try to focus an android app based on the most common software versions, Android 9.0 or 10.0 ( although Android 11 been has already reased) & hardware that is most often compatible with that level, ( e. g. Snapdragon 845 & up). At least someplace to possibly start.

Wonderful information. I already download this app in my phone. thanks you for the sharing more information. CAPT Chucri

This article states “Of the 192 apps the team examined, only 4 iOS apps met the outlined criteria for functionality, features, and calibration capability”. Unless I am misreading your cited source, the number of iOS apps that met the criteria should be 10, with 4 being the number of the Android apps partially meeting the criteria. Please correct me if I’m wrong though.

Thank you for the comment, Andrew. You are correct, we looked at 192 iOS and Android apps, we selected 10 iOS apps, and of those 10, only 4 iOS apps met our testing criteria. We modified the second paragraph above to improve clarity.

Do you have specific recommendations for external microphones?

Please see our study on external microphones http://asa.scitation.org/doi/full/10.1121/1.4964639, we examined the MicW i436 and the Dayton Audio iMM-6. Both microphones performed well in our study, though each has its pros and cons which we detail in the study. We have also evaluated the Etudige EIM-003 for our study, though that microphone does not fit the typical ¼” adapter for acoustical calibrators. Please note that references to products and services do not constitute an endorsement by NIOSH or the U.S. government.

Love the app and I am using it on an IPAD. However, I noticed when I reset the calibration or changed it to OSHA, it said “measure must be stopped before changes…” After I make the adjustment, the app stops taking measurements. How do you restart it? I close the app and go back and still not measurements are recorded.

The only way to get it to work is when I uninstall and re-install the app.

We are glad you are liking the app. For technical assistance please send a request through NIOSHNoiseresearch@cdc.gov. Please include the model of your device and iOS version.

app loaded fine and worked well. then stopped working. deleted and reloaded the app several times. on the main reading screen (Instantaneous level (dBA)) I have red text that says “overload.” Now what?

A new update of the app will be released tomorrow and will address this issue. Sometimes there is a conflict when another app is trying to use the microphone. In the meantime, we suggest closing the app completely (press home key twice then swipe the app screen upward to close it) and then try again.

You might expect a manufacturer of noise measuring instrumentation to launch into a negative, stereotypical tirade but at Casella we understand the ubiquitous nature of the phone app and we fully support anything that generates more awareness of noise in the workplace. Two comments however. Firstly I would recommend the use of an acoustic calibrator such as our CEL-120/2 with a 1/4″ microphone adaptor . Secondly had you considered resurrecting the Type 3 Indicator grade of instrument classification that existed in ASNSI S1.4-1971 (and BS EN 60651) back in the day? Since current US & EU noise legislation would not recognise the results of a type 3 instrument, it would both legitimise and caveat their use.

Thank you for your comment. We agree regarding the use of acoustical calibrators, at the expense of repeating ourselves, we wrote above “we recommend that those interested in making proper noise measurements use an external microphone that can be calibrated with an acoustical calibrator for improved accuracy.”

The issue regarding resurrecting ANSI S1.4-1971 would be up to ANSI.

We remind readers that references to products and services do not constitute an endorsement by NIOSH or the U.S. government.

With regards to android, couldn’t you just release it and ask folks to either use a calibrated external microphone or to calibrate their device’s mic?

Also, have you seen audiotool? It was around when you guys did the 1st study, on both Android and iOS, and looks like one of the more serious, full featured apps available. Puzzled why it wasn’t included.

Thank you for the comment, it’s not as simple as releasing an app on Android and then instructing people to use it with an external mics – some people may not go through the NIOSH links or see our instructions. To release this app, we had to test it on all available iOS devices and ensure that they all perform according to our criteria, with the built-in microphone and with external microphones.

As for your other question, If you are referring to the AudioTools app, we did include that app in our studies. If you are referring to AudioTool, that app did not meet our selection criteria for occupational type of noise measurements.

I downloaded the app and let it run for a few minutes in the office. Worked fine. The next time I tried the app It did not seem to work and shows in red letters “overload”. What is going on and how can I restore operability?

New update to address this issue should be available today, in the meantime, try closing it completely by pressing the home button twice and swiping the app screen up.

Great app! I have downloaded it to my iPad too. No problems whatsoever. I love the way it goes immediately to the SLM mode . Is there a way to attach a picture to the email?

Thank you for the input, David. You can share the noise report, in pdf format, via email. If you like to attach a picture of the screen, then I would take a screenshot (using the home and ON button) and then in the email screen that has the pdf report, I would add the picture as an attachment. It’s a great suggestion, we may consider making this process simpler in upcoming updates!

Excellent app, I tested it in the worked areas with different nivels of noise, using an IPhone 7 plus, and comparing the results with a professional equipment; the results was very close (+/- 1dB compared with the professional equipment). I found a little bit more difference in closed areas than in open areas.
Nice app!!

Great idea and achievement. However, the fact that it is only for iPhones limits its use. Also, it sounds like recommending the iPhone. I know that this is not your intention at all, but still. Please review your decision to exclude the Androids!

Thank you kindly Alberto, and great to hear from you! We provide a brief explanation in the FAQ section here: https://www.cdc.gov/niosh/topics/noise/app.html on why the app is only available on iOS devices and not for Androids.

Basically, there are many Android manufacturers and each manufacturer has their own set of specs and different parts and chips that they use, not to mention the many different Android OS’s out there. In addition, some Android makers use their own audio processing, some use third party, which can introduce latency in some devices. On the other hand, Apple devices have a common software architecture called Core Audio that makes dealing with audio signals uniform across all its devices. In our studies (see the blog references above), we would find the same app provide different readings on different devices and this could also explain why the sound measurement apps market on Androids is much less developed as far as features and performance than you can find on iOS. To release the app on Android devices, we would basically have to test and verify the performance of the app on every Android device out there, all with different combination of Android OS’s as well, an impossible task at this time. We are exploring several options at the moment since we recognize the importance of the Android market.

If you, or any of our blog readers, have any suggestions or ideas for dealing with this issue, we definitely welcome them.

First I want to thank Captain Kardous and his colleagues for the studies and hard work that lead to the development of this app.

@Alberto Behar
As explained by the Captain, recording apps for Apple devices are designed around a very well build low-level API (Core Audio). Apple gives the app developers access to this low-level API through a framework (Audio Toolbox or Audio Unit). This architecture makes it easier to deal with raw PCM data (audio signals) recordings uniformly across all the devices as Core Audio isn’t affected by the hardware. Microphones and other electronic components used in the iDevice is what can change. However, Apple is doing a good job at choosing good quality parts and variations between iDevices (for the kind of measurement we are looking for (peak values of PCM data)) can be corrected with proper calibration. Apple has much less SKUs than the entire Android market, making it easier to find the variations in the lab and correct them.

Also, Android devices are subject to more latency in the audio signal processing. The main reason for that is that the low-level API (OpenSL ES) for audio recording is not very well integrated across all the operating system versions. Also, OpenSL ES is missing some features that requires some hard work in C and C++ language to code the desired calculations. Developers are using public JAVA APIs instead (AudioRecord or MediaRecorder) that has huge audio latency and might not be suitable for real-time measurements.
As for the hardware part of the issue, there are more than ten popular Android phone brands on the market, all using various components.

All things considered, it is indeed an impossible task to test and verify the performance of the app on every Android device on the market to find a proper calibration.

How can I get permission to have the article posted in Canadian Audiologist, where I have a column (“Noisy News”)?

Thanks

All of our products are in the public domain and available for use free of charge. Please feel free to reprint the blog post. We just ask that you provide the correct attribution.

Really nice article and good information

I have asperger and workshop in an Office environment. I would like to use this tool to measure the total sound dosis received every day. For concentrated work the advised level is about 45db or less. That is a much lower than the level for hearing damage. Is it possible to add these lower levels to the app so we can use it also for office sound level dose? Is there a way that I calculate the dose myself for this lower level based on 80 db? I’m also thinking about sharing the data between colleagues. Would be handy if the data could be exchanged in binary format with some kind of service for reporting on a larger scale. Think about the best office to work for contest.

Thanks for your comment, Tauvic. The app was designed to measure noise exposure in the workplace and is aimed at industrial hygienists or occupational safety and health specialists. The 45 dB is a non-occupational limit for office environments and indoor spaces and thus it is beyond the scope of our mandate at NIOSH. There are instruments out there that allow you to set the threshold at 40 dB (or no threshold at all), there is no way to calculate the dose otherwise, unless you find a way to record the actual sound waveform in your office and do the calculations based on that recording of the raw signal.

Thank you for the suggestion for using binary data, this is something that we might consider in future updates.

I am getting an error message that says “Overload” when I open th application. How do I remove or clean up the “Overload?”

Please see the January 24th response to Marc. An update is now available for the app which addresses this issue.

I found a bug at the report.
After configuring the threshold limiter to 80dB.
At TRESHOLD information is written 40dB instead 80dB

If you download the latest update (3/2/17) you’ll see that the issue has been corrected. Thank you.

I have noticed that if I use my Iphone 6 without using an external microphone, I get noise levels which are much lower than the actual sound levels.

If I use my ipad ai without using an external microphone, I get much better results and higher noise levels.

Anyone else, notice this?

I have noticed this as well. I also get higher readings with my iPad to a degree of about 10 decibels. I don’t use external mice but have ordered one to see if there is a difference as well. Which one should I use?
Thanks.

Hi all,
I’ve reinstalled the app as I also had problems with the message ‘overload’. However, the message is still there! What should I do to make this work?

Some users have reported this ‘overload’ problem and it’s due to the interface not refreshing. We’re aware of this bug and we’re working on a fix, expect a new update soon. In the meantime, please try to turn off your iPhone and let it reboot and it should have resolved it.

I haven’t downloaded and tried the app yet, but it seems intended mainly for handheld use with a user in constant attendance.

Some kinds of noise exposure happen infrequently or unpredictably. For example, neighborhoods near me have started experiencing increased noise from overflights connected with a large airport within five miles, as air traffic routings and protocols are modified to exploit the potential of GPS. Noisy overflights happen unpredictably, so it would be useful to have the measuring device in standby mode, tracking noise levels, and springing into more intensive action when a threshold is exceeded.

Beyond measuring the levels for a single weighting, it would be more useful if enough information could be retained so the levels could be calculated and displayed under multiple weighting schemes and different metrics, e.g. instantaneous maximum, L10, L90 and so forth. It would also be good to save recordings of noise incidents, perhaps including some seconds before and after the actual threshold-exceeding period.

The overflight example is only one scenario. Others that have come up in my neighborhood have been late-night street racing, construction noise, loud custom mufflers and freeway noise. A smartphone-based application for extended monitoring would be extremely helpful in all these instances and surely many others.

Hello Dave and thank you for the comment, you bring up some interesting points.

It’s true, the app is intended for the user to be in constant attendance. Our aim is to help the occupational safety and health specialist make an easy and quick noise measurement in the workplace – the app measures and calculates the relevant occupational noise exposure metrics and reports noise levels and averages in A, C, or Z weighed decibels. The user can also save measurements, generate reports, or upload/share those measurements.

As for your suggestion to have the app running in the background constantly and then records events when certain thresholds are exceeded, while possible, it would most likely require a dedicated smartphone – no phone calls or running any apps that need access to the microphone, very careful handling (can’t be taken in and out of pockets and such), and most importantly, different features since our app is intended to measure occupational noise instead of environmental noise. I believe there are some studies that have used smartphones as dedicated sound measurement tools. Some researchers have explored the use of older, refurbished smartphones with a dedicated app, to build a cheap noise monitoring network, mostly in urban settings. I believe limitations regarding battery life, proper calibration, and reliability continue to hinder their wide adoption for more than conducting research studies though.

I just tried to download the App. However it is not available from the iTunes nor from the App Store. Any reason?

It is available, you will need to search under NIOSH or NIOSH SLM and it should be the first result. Or you can click on the direct link above.

Thank you Capt Chuck and Metod for this great app! Is there a way to display the frequency spectrum of measured noise in this app? If not, can it be added in future versions?

Thank you for the kind comment, Dr. Deshpande. There is no current plan to display the frequency spectrum though we may consider it if there’s enough interest. There are some apps out there that offer frequency spectrum, check our earlier study on smartphone apps http://asa.scitation.org/doi/full/10.1121/1.4865269, several of the apps we tested offer various displays. For instance, NoiSee from EA LAB, our partner, offers octave band display. SPLnFFT (Paid app) offers Octave and FFT displays.

I am having trouble reusing it. It says overload…

Some users have reported this ‘overload’ problem and it’s due to the interface not refreshing. We’re aware of this bug and we’re working on a fix, expect a new update soon. In the meantime, please try to turn off your iPhone and let it reboot and it should have resolved it.

Endless possibilities makes me even more curious. Wonderful insights here at you blog.
Very informative post. Nice collaboration, keep it up.

Good to see the NIOSH app. I compared it using the SoundLog app on an iPhone 5S and the standard internal microphone. The NIOSH app seemed to be consistently low by about 8dB compared to an inexpensive sound level meter, a UNI-T UT353.The SoundLog results were within +/- 1 dB of the UNI-T.
Sound levels were provided by a 1000Hz tone produced by a loudspeaker.

All uncalibrated – so the could explain a lot 🙂

You might want to test the SoundLog app. It has some nice features/

We have tested the NIOSH SLM app in our lab to verify its operation over 65+ dB range, see videos in links below when we compared it to a type 1 professional grade sound level meter.

https://twitter.com/NIOSHNoise/status/822186936093868035

https://twitter.com/NIOSHNoise/status/822174014063972357

The SoundLog is an excellent app from the National Acoustic Laboratories, an Australian government research institution that conducts research on noise and hearing loss, similar to the NIOSH hearing loss prevention program. SoundLog displays the LAeq (A-weighted, equivalent sound level), LCpk (C-weighted peak sound level) and LAeq.8h (A-weighted, equivalent sound level averaged over 8 hours). Our app displays the instantaneous sound pressure level as a default (in A, C, or Z weighting), but you can select to display the LAeq, Max Level, LCpeak, TWA, and Dose. So when you do comparisons, I suggest comparing the LAeq on both apps, I just ran a quick test (pink noise through speakers) and the LAeq on both apps are with 1 dBA of each other’s and with the Larson-Davis model 831 Type 1 sound level meter.

Thanks. I will have another go at my comparisons. I understand that you have done lots of tests for the NIOSH SLM showing it is a robust app 🙂

GUI of this /sound level meter app is fabulous, I found its user interface something like M Indicator app even you can compare it

This app is amazing.

in word NIOSH app is simply amazing!!!…

What about us Android users? You’re just going to leave us without this wonderful tool?

We are exploring several ideas regarding Androids. See my response above to Alberto Behar on February 6th as to the reasons why the app is not available on Android devices. We also provide a brief explanation in the FAQ section here: https://www.cdc.gov/niosh/topics/noise/app.html

When I use my iphone with no external mike I get a lower reading then when I use in the same way my iPad Pro (around in average 10 decibels)How can this be explained? My iPhone is a SE.

We have tried to see if we can get different readings on our iPads and iPhones in our lab to measure various noises, but have not seen similar results. Only at very low ambient background levels, there’s some discrepancy between the iPad and the iPhone readout but that can be explained by the different sensitivity of the microphones. Are you running the same OS on both devices? Also, the iPads have a back-facing noise-cancelling microphone, in addition to the front-facing one that may be causing some issues for some users. Try to go into Settings, General, Accessibility and see if the Noise Cancellation is enabled or disabled on both devices?

I was wondering if the NIOSH Sound Level Meter App source code for the iOS is available or is public domain?

This product was developed under a Memorandum of Understanding with an outside partner so the code is not in the public domain.

Thanks for sharing this post. Android’s source code is released by Google under an open source license, although most Android devices ultimately ship with a combination of free and open source and proprietary software, including proprietary software required for accessing Google services. Android is popular with technology companies that require a ready-made, low-cost and customization operating system for high-tech devices.

What type (make/model) of external microphone and calibrator should be used to achieve the + or- 1 dB error rate?

Hello Emily and thanks for your interest. In our study, we evaluated two microphones, the MicW i436 and the Dayton Audio iMM6. Both microphones performed well over the 65-95 dB (pink noise) testing range in our lab, when calibrated. We used the Larson-Davis CAL200 acoustical calibrator in our study.

that app availabe on playstore ?

No, app is only available on iOS devices. Please see one of our comments above regarding the reason the app is not yet available for Androids.

Nice Blog! Thanks for sharing very useful post. keep it up.

Great app. That said, I tried using it to measure rifle gunfire with and without a suppressor and the results were too close. Is there suggested settings for short peak impulse sounds? Thanks!

Thank you, Max. Measuring peak impulse sound levels, especially from gunfire, require some dedicated and specialized equipment. We’ve done some studies in the past where all of our noise dosimeters clipped above 143 dB SPL. Gunfire can measure anywhere from 160-170 dB, and the highest level we were able to capture with the app is 139.2 dB SPL. In other words, this app – or any smartphone app for that matter – cannot capture peak sound levels accurately.

A question regarding ready-calibrated external microphones – does this model measure up to the 2 tested microphones, here earlier mentioned? In your opinion, any heads-up compared to those tested by you? I have your app and I can’t wait to get started with using an external mic.
http://www.rationalacoustics.com/wp-content/uploads/2015/07/iSEMic-725TR-datasheet-USletter.pdf
All the best, Martin @ https://desiderata.xyz

Hi Martin, thanks for bringing that specific microphone to our attention. Not having tested that specific mic, I can’t offer any empirical judgment. However, I would tend to think it will work as well as the mics we tested, it has excellent specifications and the manufacturer claims it is IEC 61672 class 2 compliant. The main point with any of these external microphones, is the ability to calibrate them using commercial acoustical calibrators and available adapters (a 1/4” adapter would work perfectly with this mic). It doesn’t look like it offers a lightning port adapter so will not work with iPhone 7 and later.

In your response to Martin you state “It doesn’t look like it offers a lightning port adapter so will not work with iPhone 7 and later.” Is that true? iPhone 7, 8 and X all come with an adapter for “lightening port-to-audio jack.” Wouldn’t that solve the problem and make it work for the later iPhone models?

Great question, Frank. Yes, it is true that newer Apple products do come with a lightning port to 3.5 mm headphone jack adapter. The issue with that arrangement is that it will leave the microphone ‘dangling’ from the adapter. To make a good noise measurement, the orientation of the microphone is important and a dangling cable (and microphone) may present some issues to how the user handles and orients the microphone. Some microphone manufacturer make microphones that can plug directly into the lightning port (e.g., MicW’s i437L and Studio Six Digital’s iTestMic2). The microphone mentioned above by Martin, does not seem to offer a lightning port adapter that can be directly plugged into newer Apple devices.

See photos 1 and 2

Love the app, but I found it only after doing an online search for sound meter apps. Your app would likely find a broader audience if the AppStore listing made it more findable. For example, consider calling it “NIOSH SLM Sound Level Meter.” Cheers!

Thank you for the kind endorsement of the app, Steve. We have received similar comments in the last several months from users having a hard time finding the app, and now with the introduction of iTunes 12.7, Apple has removed access to the App Store from its desktop versions, so that makes it even harder for users to find our app without using specific search terms. We are still learning how App Store users search and find apps so this suggestion and feedback is very valuable to us and we will consider it in the new update we’re currently working on!

Will the app recognize microphones plugged in directly to the Lighning port like the MicW i437L mentioned above? We had tested a consumer Sennheiser microphone with a lightning connector on an iPhone8 about 4 months back, and it wasn’t recognized at all.

Thanks.

Yes, the app will recognize an external microphone automatically, we have tested it with the MicW i437L and SSD iTestMic2. Please let us know if you still encounter any issues, and the model of the Sennheiser microphone you use.

If this is the Sennheiser MKE2 Digital, it already processes the noise signal to a digital data stream, bypassing the analog input, and presumably the NIOSH software.

Dear Captain Kardous,
Could you please speak to changes in the newest update, specifically regarding the “dose?” While in the immediately previous version, “dose” was a running tally, and “projected dose” an extrapolation of that measure over 8 hours, the basic “dose”measure now appears to be the latter. For example, in the older version, if I whistled directly in to the mic, dose would slowly rise 1, 2, 3, etc. %. Now doing so spikes the dose well over 100%. This value drops the longer the recording continues, as quieter readings are averaged in.

The documentation does not seem to address this change (although in the help page of the new version there is only one landing page and no further info?).

All best, and thanks to your team for their hard work on this app!

Dr Ian Howell
New England Conservatory
Boston

Dear Chuck, I’m just starting to use your App for noise monitoring at home. I know the App is set for industrial purposes but I think it suits my purpose. Our local Government sets the recommended noise level for residential areas at LAeg, adj., 1hr. I’m not sure if that’s equivalent to the LAeq set in the NIOSH App. Could you advise?

regards
Greg Palmer

Dear Greg, so it seems that your local government is setting LAeq, the A-weighted, equivalent sound level (average level) measured over 1-hour period. If you plan to use the NIOSH app, my suggestion is to run it for exactly one hour and report the LAeq value (third row). You can also press the LAeq and it will appear at the top for easier reading. Make sure you save the measurement(s) using the save button at the bottom after each 1-hour measurement so you have those records.

Can the app not export a .cvs or .xls of data points with a timestamp?? That seems more informative to me than a report of what the max, peak, etc is.

Thank you for your suggestion, Suzi. We’re always looking for ways to improve users’ experience so we will take your suggestion into account for a future update. Right now, you can save the measurement with a timestamp (date and time, along with a measurement duration), and share it in .pdf and .html formats. Saving data points may require additional permissions and availability of adequate storage on your device.

Nice information

While the app recognizes the MicW and itestmic2 when attached thru the lightening port on new iphones, have you tested whether measurements are the same as having the mics on the headphone port, assuming that the position of the mic on the cable is stable and oriented to the sound source ( re your earlier comment)

Yes, we have tested the NIOSH SLM app with new external microphones that connect directly to the lightning port, including the MicW i437L and SSD’s iTestMic 2. The MicW microphones work very well out of the box (within 0.3-0.5 dB SPL when calibrating using an acoustical calibrator). The SSD iTestMic2 did not perform as we expected with our app, or another reputable SLM app.

Dear Chuck,
is the NIOSH SLM app suitable also for measuring low frequency noise, i.e. 100 Hz ? The large power transformers in electrical substations in Europe emit mainly at this frequency and harmonics. Maintenance workers are exposed to these low frequency components. Thank you very much.

Hello Roberto, the MEMS microphones used in smartphones (or if you use an external microphone) can measure noise levels as low as 20 Hz according to their manufacturers. For low frequency measurements, you will need to choose Z-weighting from the settings instead of the default A-weighting. However, for such types of measurements, it is best to use a professional sound level meter, with an appropriate microphone, that can provide 1/3 octave band measurement features, so you can see/display the exact contribution from such sources.

Thank you, Chuck.
Only a short reply.
Our goal is to test the suitability of apps for a very preliminary survey of noise around transformers, that can be done directly by the workers using smartphones.
If MEMS microphones are good in measuring until 20 Hz, is there some issue related with SW and with the working out of the acquired signals ? Why it is best to use a professional SLM ? Thank you.

Hi Roberto, there shouldn’t be an issue with the software of the app, all it’s doing is taking the electrical signal from the microphone, digitizing it, and applying some calculations to convert those signals into decibels. The microphone’s suitability for low-frequency measurements is the most critical component here. For a preliminary assessment, the app should be fine. You should plan to make two sets of measurements, one with the default A-weighting and one with the Z-weighting selected. You can then compare the two measurements to understand the low-frequency noise contribution from the transformers. The Z-weighted noise levels will higher, depending on how much of the noise is low-frequency. There are apps that offer octave and 1/3-octave band analysis, see the apps from our study on smartphone apps SoundMeter, SPLnFFT, NoiSee, and SPL Pro all offer some sort of frequency or octave-band analysis, at some nominal cost.

A measurement with a professional SLM is suggested if you are trying to conduct a full assessment and isolate the noise emitted from the transformers, especially if you plan to implement some engineering controls to mitigate any harmful exposures to the workers.

Love the app, but I found it only after doing an online search for sound meter apps. Your app would likely find a broader audience if the AppStore listing made it more findable.

Thank you for the valuable feedback, Husein. We are gradually trying to increase our exposure on the AppStore. We had a similar suggestion few months ago and we made some changes in the naming and keywords used, and added an option to allow the users to rate the app and that appears to have helped a bit. However, if you, or any of our valuable readers, have other suggestions for making the app more findable, we would certainly appreciate it.

I measured my guitar amplifier with an iPhone 4S internal microphone at 72db. However, the ear that is closest to the amplifier feels muffled. Is there any chance that I’m damaging my hearing?

Hi John, it’s not likely that exposure to 72 dB is going to cause hearing damage. Our recommended exposure limit is 85 dB (A-weighted), and that’s over 8-hours a day, 40 hours week, and years of exposure. We do recommend hearing protection for sound levels above 85 dBA. Questions I would ask, how far was your iPhone from the amplifier speaker, was it pointed (bottom side where the microphone is) at the speaker, I would also try to take an average, you can do that by selecting LAeq and let it run for 10-15 seconds. It could be that the measurement is too low.

Having said all that, muffling in the ear is a symptom that often needs medical attention, especially if it happens repeatedly after you play your guitar. We do recommend that you follow up with a health professional, your physician or an audiologist.

Nice app i will try it

I downloaded the Sound Level meter app on an iphone 5s and and an iphone 8. When starting the app, both phones do not display a sound level and both say “Overload”. The microphones do work in other apps.
Is there a correction for this?

Hello Tom, Please make sure that you allow the app the permission to use the internal microphone, a message pops up the first time you open the app (“NIOSH SLM would like to access the microphone”), please press OK to give it permission to use the internal microphone.

If you want to use Apple’s Lightning to headphone jack with a microphone and not have it flapping in the breeze, get a MOVO Lightning Cable Dongle Adapter Clip – Amazon part B073C6VWR5

Hello;
Could you please comment on or recommend (without endorsing) an appropriately priced Type 2 field calibrator for routine calibration of the microphone.

Even with a reliable instrument and microphone, the user may benefit from knowing accepted techniques for measuring sound level with precision and accuracy.

Hi, we can’t comment or endorse any specific product, we use Type 1 and Type 2 acoustical calibrators from the main sound instrument manufacturers such as Larson-Davis, 3M Quest, and B&K among others. Those types of professional instrument calibrators are priced in the several hundred to over a thousand price range. There are cheaper options on the market but we cannot vouch for their accuracy or reliability, though they should be adequate for general purpose, Type 2 level of accuracy, noise measurements. I think it will be worth checking the manufacturer specifications for accuracy, some provide in the form of ± x dB, it is also worth checking whether the calibrator meets IEC 60942 standard or equivalent before making a purchasing decision.

One important factor in the calibration process is to ensure that you obtain a calibrator with the right adaptor. Most external microphones, especially the ones we tested, have a ¼” diameter so it is critical that the external microphone has good fit to ensure proper calibration. See image at 4:03 – 4:21 on this video https://www.youtube.com/watch?v=zk07tLj_SDs

This is great app, thank you for developing this. It is an excellent tool for informal sound surveys in the workplace. How far do you think you are from an app that can be used for compliance purposes provided you use the appropriately sensitive external microphones and calibration devices?

Hello Chris, regulatory agencies specify that a sound measurement instrument must conform to specific national (or international) standards. The sound level meter standard has 3 parts. NIOSH is making concrete steps towards establishing conformance of the app with part 3 of the standard, periodic testing, and developing a framework for others to follow. See our recent publication where NIOSH established compliance with IEC 61672 (ANSI S1.4): Part 3 – Periodic Testing, “Smartphone-based sound level measurement apps: Evaluation of compliance with international sound level meter standards.” Applied Acoustics, 139, 119-128. https://doi.org/10.1016/j.apacoust.2018.04.011. NIOSH has also conducted several field-based studies that show excellent agreement with professional sound measurement instruments, when used with external, calibrated microphones.

However, a sound measurement system must comply with a host of acoustical, electrical, and environmental requirements to fully meet standards. This is typically accomplished by sound instrument manufacturers. Although we did develop the app software, NIOSH does not manufacturer the hardware that it takes to make the system, as a whole, compliant with the standard.

Thank you for your interest in the app and your support.

Helped me a lot, I was looking for this information, thank you for sharing.

Hi just to let you know that, iPhone XS displays about 10 dB lower value compared to iPhone 6s. Regards,

Thank you for the heads up, we are working on a new update for iPhones XS and XR models, as well as some other enhancements to the app, the new should be available within a week or two.

I notice that manufacturers of external microphones such as the iMM-6 also offer free calibration files. Can such files be loaded into the NIOSH SLM?

Hi John, great question. We have tested some apps that support downloaded calibration files and found that such files did not improve the accuracy of the calibration when compared with using acoustical calibrators. It appears that such calibration files are based on some “nominal” correction values and are not specific to the external microphone’s sensitivity and frequency response – which would be required to establish proper calibration.

The NIOSH SLM app will automatically select a “nominal” correction value when a user plugs in an external microphone, and that value is based on our testing and evaluation of external microphones’ sensitivities. We recognize that this is not an optimal solution for establishing proper calibration and that is why we continue to recommend calibrating external microphone with acoustical calibrators similar to how an industrial hygienist or an occupational safety and health specialist (our main target audience) would normally calibrate their instruments prior to use. We believe this is the best practice until a calibration standard for smartphone apps is established.

I forgot to add a second question. Basically, does it matter. That is, does the use of a iMM-6 microphone , as is without calibration with a reference source or the use of calibration files, provide any advantage to the performance of the NIOSH app?

Chuck, Thank you for the prompt and clear response. I assume that you are also using a nominal correction value for the internal microphone. Given that is true, should one expect the use of an external microphone would have accuracy equivalent to that of the internal microphone? Or, perhaps, because there may be more uniformity among iphone microphones, I should simply stay with using the iphone microphone. Sorry for being such a nit pitcker.

Hi John, yes we use a nominal correction for internal microphones. And yes, we provide a correction for external microphones based on our testing of 10+ external microphones. The use of an external microphone does not add to the accuracy per se, we recommend it because you can calibrate it with an acoustical calibrator. Out of the box, it is not necessarily better than the internal microphone on a new and well-maintained iPhone that is not exposed to the elements. However, on an older iPhone where the internal microphone has been exposed to various environmental elements (humidity, temperature variations, dirt accumulation at opening, etc.), the external microphone will be a better option.

A highly useful app when it comes to sharing noise data through smartphone to relevant sources. Developing a noise exposure monitoring mobile app is a must need for every primary and secondary industry segment. It can significantly help to bring noise pollution under control across various parts of the worlds prevalent due to human error.

Would like suggestion on microphones for iPhone XS Max and update on how to use it with the app.
E’s Nov 14, 2018 message had suggestion that sound levels were 10 dB lower. Is tuning required?

Hi George, the microphone shown in the images on our website is the MicW i437L (L stands for Lightning). It’s the same microphone that we tested in our study https://asa.scitation.org/doi/full/10.1121/1.4964639 but this one works with lightning ports. The app recognizes the external microphone automatically and assigns it a nominal sensitivity based on our laboratory testing. We made a couple of updates to the app since November 2018 to address the issue with the iPhone XS, so no additional “tuning” is required.

Hi, great app! I was wondering whether there was any way to get people’s individual app data downloaded to one cloud. To be more specific, if I were to ask people to put the app on at various times of the day, is there a way for me to get their app data without me having to ask them to report it themselves? I hope this question makes sense. I would be happy to clarify further.

Hi Katrina, Thanks for your interest in the app. There is no way to upload noise data to the cloud currently, or to allow others to view it. We are exploring several ideas to expand the functionality of the app, including crowdsourcing and noise mapping. Stay tuned. If you have specific ideas or suggestions, we would be happy to hear them.

I think you should reconsider your decision not to develop a companion app for Android devices. Since Android clearly dominates the market it does not make sense to exclude 3/4 of the market from an app that would benefit everyone, not just IOS users.

On the MacWorld UK site I found the following:

For the period from Jan. 2018 to Jan. 2019 Android accounted for ~74% of the market, and iOS comprised most of the remainder at ~23%. The remaining ~3% was comprised of KaiOS, Windows, Samsung, and a trace of other unknown systems.

So you’re only reaching one out of four people and ignoring a huge slice of the population.

Hello Bob,

We recognize that the Android marketplace is much larger than the iOS market, especially outside the U.S. However, the Android platform is fragmented with many manufacturers and models, each using different components: audio chips, microphones; even within the same manufacturer. Each combination of software, hardware, and sensor (microphone) have different sensitivities and response characteristics. Assuring the accuracy and precision of the NIOSH SLM app across the many permutations within these devices is very challenging. We have not yet solved the problem, but we are considering some possibilities. For now though, we are limited to the more uniform iOS platform.

Great Post!

Can I buy a 2nd hand Apple phone to use this noise app?
How far back in time can I go (to lessen the price of the 2nd hand Apple phone)?

The app will work on older models although it’s optimized for iOS 11 and higher, which according to Apple, is iPhone 5s and higher models.

Greetings! I am an Industrial Hygiene student and I got an assignment in which I need to download this app in order to obtain the data of three sources I need to measure and make calculations based on it. Unfortunately, I don’t have an Apple device at home to download it. It would be great, and I suggest, for the application to be compatible for Android users like myself; I also feel it would be good because more people would be able to use it regardless of what phone model they got. I hope you can take it into consideration. Have a nice day/night! 🙂

Is there a specific distance the iphone’s microphone should be placed from the sound source to get an accurate reading?

Asking as I have placed my iphone 1 meter away from the sound source as well as a few inches away and the readings are substantially different.

Hi George, it all depends on the source and the type of noise generated, but typically we recommend holding the phone or if you’re using an external microphone about 1 meter away from the source, and away from any obstructions. There’s a small section in the help menu called “How to conduct a noise survey” that you may find helpful.

As for the change in sound levels vs. distance, that’s governed by the Inverse Square Law as you may already know (sound pressure drop of ~ 6 dB with doubling the distance from the source).

Hi Chuck,

Thanks for your all your work. Why not port a version of this app to the single largest Android mobile device platform, namely Samsung Galaxy, which accounts for 32% US market share for Q3 2020 (compared to iOS 46%)? By adding this single port you provide a meaningful amount of Android device support and dramatically increase your platform reach by almost 70%, while avoiding the challenges in supporting the dozen or more other Android platforms comprising the remaining 22% of the market.

Thank you for your comment. That is how we would ultimately like to proceed.

Hi, It is great app!
looking the photo at the beginning of the text, Ι wonder if an external microphone that has a calibration file can be used or there will be such an event in the future

As we mentioned in a prior response, we have tested some apps that support downloaded calibration files and found that such files did not improve the accuracy of the calibration when compared with using acoustical calibrators. It appears that such calibration files are based on some “nominal” correction values and are not specific to the external microphone’s sensitivity and frequency response – which would be required to establish proper calibration.
The NIOSH SLM app will automatically select a “nominal” correction value when a user plugs in an external microphone, and that value is based on our testing and evaluation of external microphones’ sensitivities. We recognize that this is not an optimal solution for establishing proper calibration and that is why we continue to recommend calibrating external microphone with acoustical calibrators similar to how an industrial hygienist or an occupational safety and health specialist (our main target audience) would normally calibrate their instruments prior to use. We believe this is the best practice until a calibration standard for smartphone apps is established.

Chuck,
I enjoy using the NIOSH SLM app, especially having read your published research demonstrating its accuracy. It is my preferred and go-to app for estimating sound levels. I currently use it on an iPhone SE2020 and look forward to your testing the app with that phone. My rough check at home using broadband noise and comparison to a Quest SLM suggests that a +8.5-dB correction is needed when using the phone’s internal mic so I have “dialed” in that correction factor..

I have one feature request for an enhancement. Please provide a means for an easier switch from A weighting to C weighting for the instantaneous sound level, perhaps a toggle to the right of the larger number at the top, and/or displaying both the LAeq and LCeq on the same row in the third row down of the main display.

Again, thanx for the great work on the product.

Thank you for your support and the kind words, Elliott, it means a lot coming from someone with your distinguished research background. We have not had access to our labs to test the accuracy of the app on the latest iPhones (that were released late in 2020) due to COVID, but we’re planning to start doing so shortly and releasing a new update.

Thanks for the feedback about the new features, some great suggestions. We hope to continue to improve the app and add new features as our time and budget allow, stay tuned.

Hi,
I have downloaded the app on to my iPhone but it opens saying that it needs permission to access the mic and go to settings but when I go to settings & microphone the app is not listed as one requesting access – any ideas how to resolve?
Thanks

Hi Tim,

The first time you launch the app after you download it, a small screen will pop up asking you to get permission. But, if you select no or ignore it, you can do so from the Settings screen, go to NIOSH SLM app in Settings and allow access to the microphone.

Hi, I run the app on an iPhone 6 plus and an iPhone 12 pro.
On the 12 pro, SPL readings come in about 10dB lower – pretty significant.
The 6 plus readings seem about right.
Calibration settings are identical (+/- 0) for both devices.
Can you update the app for microphone sensitivity/amp output in different devices? At 10 dB the app would have to see a voltage from the mic that is 90% lower for the iPhone pro. Is it picking the signal up at a different stage in the path (pre-amp)?

We have a new update coming that will address the latest iPhones.

This is truly an amazing post. Good Job. Keep it up!

Been looking for reliable sound measuring app that I can load onto my mobile. VERY surprised and disappointed to see that the app developed by NIOSH is only (?) available for apple; no progress toward an andriod compatable app (2017-2021)?
When can we expect the reliable NIOSH app for android? (hopefully soon!!)

We are aware of the demand for an android version of the app. At this time we cannot commit to a production schedule.

When can we expect the reliable NIOSH app for android?

We are aware of the demand for an android version of the app. At this time we cannot commit to a production schedule.

We are trying to measure the sound coming from a loud bar/nightclub. Can an iPhone be used with your app for that purpose? Attempting to measure the noise from approximately 100 feet away.

Is there a way that the iPhone (11 or 12) can be easily calibrated to produce accurate results? In particular, results that would stand up to scrutiny by a municipal authority?

Would this app be usable by local police to measure the sound level when responding to noise complaints? Many police officers carry iPhones.

Thank you for your comment and three questions. I would like to preface my answer with a disclaimer that NIOSH research on the NIOSH Sound Level Meter (SLM) app was intended to evaluate their use for assessing workers exposure to excessive noise, but was not focused on compliance and enforcement. NIOSH research showed the accuracy of the app to be within +/- 2 dBA using the iPhone’s internal microphone. However, when we tested the app with an external calibrated microphone, we were able to achieve greater accuracy, around +/- 1 dBA, which is equal or better than commercially-available Type 2 sound measurement instruments. So the answer to your first question about calibration is yes, it can be calibrated to produce accurate results to the extent documented in our recent paper (https://asa.scitation.org/doi/full/10.1121/1.4964639). We also examined the performance of the app for compliance with the IEC 61672: Part 3 international standard for sound level meters when used with an external calibrated microphone (https://www.sciencedirect.com/science/article/abs/pii/S0003682X17309945), however, calibration requires the availability of an acoustical calibrator to the person conducting the measurement, which is more readily available to professionals who practice in the field of occupational safety and health.

In regards to whether the measurement would stand up in a court challenge by a municipal authority, that is a legal question for which we have no basis to comment, and which may vary by jurisdiction.

Is the NIOSH SLM app usable by local police when responding to noise complaints? Possibly, yes. At a minimum, local police may be able to use the app for screening (range-finding) purposes to assess situations that are clearly below the applicable standard, at which point no further follow-up would be needed; or if they assess the situation to be close to or over the applicable standard, they can then bring in the “official instrument” that is used to document noncompliance to make the formal assessment.

August 24, 2021 My neighbors and I are looking for a noise app for a project/problem we need to solve. When I found this one I thought: “perfect for us!”. Imagine my disappointment when I realized the app only works on an iPhone when I have an android! Seeing the number to call I did. The woman who answered also has an android and didn’t know (why would you if you didn’t need such an app?) the app was exclusively for iPhones. This is especially annoying because it is a government entity making it available. She assured me she would send my message to please make this also an android app to someone who might be able to do something about it. To my surprise, a few hours later I received a reply.

Thank you Chuck for the swift response. I hope the near future will make this app available to the rest of us who don’t want to join the Apple Community of products. And anyway why would this scientific body want to favor one platform over another? Most apps are available to both and and only a very few are exclusive to one. We can’t wait in our neighborhood but I’ll be watching for the app because noise level is something I like knowing about. Meanwhile we’ll have to settle for something without the backing of the CDC and NOISH and hope it is good enough to help fix our problem.

Thanks for your comment. We have referred your concern regarding the Android version of the app to our Noise and Bio-Acoustics team for consideration.

Just reiterating how fantastic it would be to have an Android version of this app. There are a lot of unique features in the NOISH app like the dose and projected dose that are not included in other apps which are more acoustics or sound/music technician oriented.

I, too, will say there is an urgent need for an Android app.

I am more than reasonably certain that the volume of background (so-called) music in public places has increased greatly in the last decade or so. The ability to call dispassionate factual attention to the issue would be helpful.

In 2018 I was enlighted to introduce information on the 2017 NOISH-SLM app in a course book on occupational hazards. Now I am updating this book and wonder about any progress in this field, especially if (some) android phones can be used reliably as SLM. It would be nice if NIOSH regularly updates a webpage on smartphone-SLM matters so that one can easily inform oneself on the state of art. The same might apply to the use of a smartphone as audiometer. Both smartphone applications are relevant for health care workers in low-income countries.

Whilst a very useful tool, has consideration been given to adding photos? It would be useful to generate a report that, in addition to the notes section, it would be possible to take a photo of the noisy equipment or plant and to have an actual photo of the equipment in question feature in the report.

Thank you for your comment. Due to potential privacy concerns we opted not to include this function.

Hi, another vote for an Android version please.

Hi,
Does this app work on the Apple Iphone 14 Pro? Currently I can only see a recent update for Apple iphone 13.

Thank you for your question. An update for the iPhone 14 and 14 Pro is in the works and should be ready in early 2023.

The new update to the NIOSH Sound Level Meter app is now available.

Just a heads up, on my new iPhone SE (2022 version) the app reads about 10dB low compared to a calibrated spl meter. My old iPhone 6s was within 1dB compared to the Spl meter.

Many thanks for a very well thought out app

Thanks for bringing this to our attention. A similar issue was noted recently when using the app on the iPhone 14. A new version containing fixes for all the new models (SE, 14) is currently being validated and will be published soon. We’re glad to hear that you find the app helpful.

The new update to the NIOSH Sound Level Meter app is now available.

Thank you for the new update, my new iphone se 2022 reads within 1dB of my calibrated spl meter now!

1. If the C-weighted decibel setting more reliably measures low as well as high frequency sounds is there some reason why dB(C) cannot be and is not used to assess hearing loss risk. For example, if dB(A) is based on measurement of continuous and pure tones and in contrast the brain sums a multitude of tones (low and high) and noise characteristics (e.g., intermittent noise) in its interpretation of loudness is dB(A) really reliably predicting hearing loss risk or is it perhaps underestimating the risk. 2. Are there hearing loss prevention guidelines using the dB(C) weighted curve for both impulse sound and cumulative exposure. Thank you.

Frequency weighting networks found on some sound level meters are used for different purposes. The C-weighting network provides less filtering, while A-weighing can be considered an approximation of how a person hears at very low sound levels. Empirically, A-weighting has been found to give a good estimation of the risk potential for hearing damage from exposure to continuous noise. This is why it is the weighting network used for measurements of occupational noise exposure.

Measuring impulse noise and determining its effect is much more complicated. See NIOSH Science Blog post, How Can we Measure Impulse Noise Properly? for more information.

Do you have updated recommendations for external microphones to use with this App?

I would like to view the document referenced as the “Memorandum of Understanding” in the reply comment above of Chuck Kardous on July 17, 2017 at 12:45 pm (PST?). Can you stage the document somewhere on your server and provide a link to download it?

On August 25, 2021 at 4:47 pm, there is a reply to the topic of making the application available on Android:
Blog Coordinator says:

Thanks for your comment. We have referred your concern regarding the Android version of the app to our Noise and Bio-Acoustics team for consideration.

Question: what was the conclusion of the team in regard to this concern?

I’m using your app with iPhone 14 pro to measure loudness and I’m curious what weighting to choose.

1. I produce and mix music with pair of monitors [music with high low end – hip hop and electronic] so I need to measure it with C-weighting to avoid damage?
2. When I’m driving a car [hearing wheels, ground noice, etc. without music playing] if I measure it with C-weighting I’ll get a 80-90 db, but with A-weighting 15-20 less [65-75].

So question is WHAT WEIGHTING TO CHOOSE for music production and mixing and for driving a car, in the subway, restaurant, etc.?

thank u for an answer and for your app

This comment is for the NIOSH director. I contacted you several years ago about the Android version and you claimed that you’re working on a “solution” and here we are in 2023 and still ignoring Android users. All your apps have an Android version except this one!?

In some of the responses above, you claimed that there are too many Android devices on the market to guarantee proper operation, but that’s no longer the case, so what is the excuse now for the continued delay? It is not acceptable for a government agency to continue to favor Apple and ignore 50% of the market.

Thank you for reaching out to express your continued interest in the NIOSH SLM app – particularly your interest in the development of an Android version of the app.

As you are aware, Apple iOS is a “closed” operating system, meaning that Apple maintains full control of the source code. The iOS system includes Core Audio software which facilitates uniformity in audio signals across all Apple devices. This uniformity is essential to ensuring that measurements made with the NIOSH SLM app characterize occupational noise exposures with a level of accuracy similar to professional instruments.

In contrast, the Android platform is an “open” operating system which makes its source code public, allowing users to modify it to suit their needs. Our early research showed that the same app produced different results across various Android devices. Audio performance on the Android platform varied considerably due to differences in audio chips and microphones – even within the same manufacturer. Assuring the accuracy and precision of the NIOSH SLM app across the many permutations within these devices was prohibitive.

You mention in your comment that this is no longer the case. We agree that the Android market in the U.S. has consolidated over the past several years. NIOSH has been actively exploring several options. Although we have not yet been able to develop a version of the app that would work on Android’s platform yet, we recognize the importance of this market and are continuing our efforts to make the tool available to more users. Hopefully, we can achieve that goal.

After using your app for a few days I am delighted to find it easy to use with an intuitive interface and, given its cdc provenance, have complete confidence in its consistency and accuracy.

However I did not see a way to delete saved records and wondered if I had overlooked something? Is there a way to do this?

Many thanks for providing an excellent app!

Thank you for your comment. Go to “saved measurement” and click on the measure you wish to delete. Then then swipe left. You will see “Delete” in red at the right near the end.

I would like to use the app to measure the noise level of a particular machine installed in a warehouse. While I can reduce background noise during the measurement, I can’t fully eliminate it. I can measure noise levels with only background (machine off) and then with the machine on. The Canadian Center for Occupational Health and Safety (CCOHS) describes here how to easily correct a measurement for background noise:
https://www.ccohs.ca/oshanswers/phys_agents/noise/noise_measurement.html#section-13-hdr

Is there a way to make a correction for the background noise with the app?
Is there a method similar to the CCOHS for correction of background noise to use with any sound level meters?

Thank you in advance

Hi Claudio,

You are correct, you can measure the noise with the machine on and off and then use the CCOHS method (the method is based on accepted practice when adding or subtracting noise sources) to find out the contribution from the machine alone. The app does not calculate that automatically. We are not aware of commercially-available sound level meters that can do the calculations automatically either.

Typically, sound power (or sound intensity) measurements are used to isolate the sound levels generated from sound sources, but those require special equipment and methodology that cannot be done with a sound level meter alone.

Thank you Wei Gong for your reply!

The CCOHS is a canadian institution, so I’m not sure if I can cite them as a proper source for a measurement in the USA.
If the method is accepted practice, do you know if there is a US norm or US regulation that describes it?
If not, how could I cite it or refer to it for documentation purposes in the USA?

Thank you very much,
Claudio

A background noise level correction table (e.g., https://www.ccohs.ca/oshanswers/phys_agents/noise/noise_measurement.html#section-13-hdr) is commonly used when adding or subtracting decibels. This is an acoustical principle found in noise control textbooks and not tied to a regulation or standard. Therefore, it doesn’t require any further explanation or justification, nor does it need to be cited as a reference.

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