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So How Accurate Are These Smartphone Sound Measurement Apps?

Categories: Hearing Loss, Technology

Figure 1. The SoundMeter app on the iPhone 5 (L) and iPhone 4S (R) compared to ½” Larson-Davis 2559 random incidence type 1 microphone (C).

As of June 2013, 60% of all mobile subscribers use smartphones—that’s more than 140 million devices. Apple iOS and Google Android platforms account for 93% of those devices [Nielsen, 2013]. Smartphone developers now offer many sound measurement applications (apps) using the devices’ built-in microphone (or through an external microphone for more sophisticated applications). The use of smartphone sound measurement apps can have a tremendous and far-reaching impact in the areas of noise research and noise control in the workplace as every smartphone can be potentially turned into a dosimeter or a sound level meter [Maisonneuve et al., 2010; Williams and Sukara, 2013]. However, in order for smartphone apps to gain acceptance in the occupational environment, the apps must meet certain minimal criteria for functionality, accuracy, and relevancy to the users in general and the worker in particular.

Chuck Kardous recording measurements

Video: Mr. Kardous testing mobile sound-meter apps in the lab

NIOSH noise researchers received numerous requests from stakeholders, safety professionals, and the public to address the accuracy of the many sound measurement applications available for smartphones and whether they can be relied upon to provide an accurate assessment of the ambient environment. As a result, we conducted a pilot study to select and characterize the functionality and accuracy of these apps as an initial step in a broader effort to determine whether these apps can be relied on to conduct participatory noise monitoring studies in the workplace [Kardous and Shaw, 2014]. The resulting paper, Evaluation of smartphone sound measurement application, was published in the Journal of the Acoustical Society of America.

We selected and acquired a representative sample of the popular smartphones and tablets on the market as of June 2013. Smartphone apps were selected based on their ability to measure occupationally relevant sound level values. A total of 130 iOS apps were examined and downloaded from the iTunes store*, of those, 10 apps met our selection criteria. A total of 62 Android apps were examined and downloaded, however, only 4 apps partially met our criteria and were selected for additional testing. As a result, a comprehensive experimental design and analysis similar to the iOS devices and apps study above was not possible.

The measurements were conducted in a diffuse sound field at a reverberant noise chamber at the NIOSH acoustics testing laboratory. For our experimental setup, we generated pink noise with a 20Hz ‒ 20kHz frequency range, at levels from 65 dB to 95 dB in 5-dB increments (7 different noise levels. Reference sound level measurements were obtained using a ½-inch Larson-Davis (DePew, NY) model 2559 random incidence microphone. Additionally, a Larson-Davis Model 831 type 1 sound level meter was used to verify sound pressure levels. Smartphones were set up on a stand in the middle of the chamber at a height of 4 feet and approximately 6 inches from the reference microphone as shown in Figure 1.

Figure 2. (a) Box plots of differences in unweighted SPLs between reference microphone and app.

Overall, the results in Figure 2 show that for A-weighted sound level measurements three apps had mean differences within ± 2dBA of the reference measurements. For un-weighted sound level measurements three apps had mean differences within the ± 2 dB of the reference measurement. Since national standards and occupational guidelines specify that type 2 sound measurement instruments have an accuracy of ± 2dBA, some of the above-mentioned apps could potentially be used in the occupational setting, especially if they’re used in conjunction with a type 2 external microphone such as the MicW i436.

Android-based apps lacked the features and functionalities found in iOS apps. This is likely due to the iOS advanced audio capabilities compared to other platforms, the open ecosystem of the Android platform, and having so many different Android device manufacturers using different suppliers and components.

Challenges remain with using smartphones to collect and document noise exposure data. Some of the main issues encountered in recent studies relate to privacy and collection of personal data, sustained motivation to participate in such studies, bad or corrupted data, and mechanisms for storing and accessing such data. Most of these issues are being carefully studied and addressed [Drosatos et al., 2012; Huang et al. 2010].

In conclusion, smartphone sound apps can serve to empower workers and help them make educated decisions about their work environments. They may be useful for industrial hygienists and OS&H managers to make quick spot measurements to determine if noise levels exist in a workplace that can harm workers’ hearing. The ubiquity of smartphones and the availability of these sound measurement apps may also present new research opportunities for occupational hearing scientists and researchers.

Chucri A. Kardous, MS, PE and Peter B. Shaw, Ph.D.

Mr. Kardous is a research engineer in the NIOSH Division of Applied Research and Technology.

Dr. Shaw is a statistician in the NIOSH Division of Applied Research and Technology.

*References to products, services, or apps do not constitute an endorsement by NIOSH or the U.S. government.

References

Drosatos, G., Efraimidis, P. S., Athanasiadis, I. N., D’Hondt, E., & Stevens, M. [2012]. A privacy-preserving cloud computing system for creating participatory noise maps. In Computer Software and Applications Conference (COMPSAC), 2012 IEEE 36th Annual (pp. 581-586). IEEE.

Huang, K. L., Kanhere, S. S., & Hu, W. [2010]. Are you contributing trustworthy data? the case for a reputation system in participatory sensing. In Proceedings of the 13th ACM international conference on Modeling, analysis, and simulation of wireless and mobile systems (pp. 14-22). ACM.

Kardous, C. A., & Shaw, P. B. (2014). Evaluation of smartphone sound measurement applications. The Journal of the Acoustical Society of America, 135(4), EL186-EL192.

Maisonneuve N., Matthias N. [2010]. Participatory noise pollution monitoring using mobile phones. Information Polity, 51-71.

Nielsen [2013]. Mobile Majority: U.S. Smartphone ownership tops 60%. Retrieved June 23, 2013, from http://www.nielsen.com/us/en/newswire/2013/mobile-majority–u-s–smartphone-ownership-tops-60-.html

Williams W. and Sukara Z. [2013]. Simplified noise labelling for plant or equipment used in workplaces. Journal of Health and Safety, Research and Practice, Vol. 5 (2), 18-22.

Public Comments

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

  1. April 9, 2014 at 9:29 pm ET  -   island

    So which one is recommended app?

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    • April 10, 2014 at 3:35 pm ET  -   Chuck Kardous

      NIOSH does not recommend nor endorse a particular commercial product. The data from our study “Evaluation of smartphone sound measurement applications” is available in the journal article referenced at http://scitation.aip.org/content/asa/journal/jasa/135/4/10.1121/1.4865269. The discussion section (page 189) highlights two apps — SoundMeter and SPLnFFT — that had the best accuracy over our testing range. There were two other apps — Noise Hunter and NoiSee — that were within ± 2dB of the reference sound source. Once again, note that the data results in the study do not constitute as NIOSH endorsement of any of these products.

      Link to this comment

  2. April 10, 2014 at 3:12 pm ET  -   Joselito Ignacio

    The question of any technology designed to collect data is to ask “now what” or “what do we do with this data?” If these apps, whether for noise or other occupational exposure purposes, will continue to pervade our society, a guidance document to inform public and workers on what to do with the data is appropriate. For compliance purposes, this bears serious examination since compliance may entail expensive fines or other regulatory actions. For general information to prompt workers and the public to employ safe practices and/or hearing protection until detailed analysis with actual noise survey equipment is prudent. NIOSH should seriously consider producing this guidance.

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    • AUTHOR COMMENT April 11, 2014 at 12:20 pm ET  -   Chuck Kardous

      Thank you for your comment. You are correct that compliance officer measurements will still need to be made with calibrated survey meters, not smartphone apps. Additionally, if an employer is considering large investments in noise control equipment they may wish to employ professionals who have more complex analytical instruments to assure the control designs are efficient and effective. Nevertheless, smartphone apps can serve a useful function as range-finding devices and may help workers make educated decisions such as knowing when to seek help or use hearing protection; and they may be useful for industrial hygienists and OS&H managers to make quick spot measurements when a professional survey meter is not available. Many years ago NIOSH did publish an “Occupational Exposure Sampling Strategy Manual” which is still available on the Internet at: http://www.cdc.gov/niosh/docs/77-173/pdfs/77-173.pdf. It describes the use of range-finding instruments and also strategies for monitoring compliance and enforcement. While the 1977 manual didn’t envision using smartphones, the strategies in that old document still apply for sampling and may guide the use of survey data. NIOSH is in the process of updating the Occupational Sampling Strategies Manual. We will consider your suggestion for updating our guidance on data analysis. NIOSH is also in the process of standing up a virtual center that will focus on guidance documents with respect to direct reading monitors and sensor technology.

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  3. April 10, 2014 at 3:17 pm ET  -   Ronald Hoevers

    As an industrial hyginist and safety engineer I’ve done research on this field in 2013 as part of my bachelor safety engineer. I’ve witten a thesis with the title ‘smartphone as an Oh&s professional’ (in dutch). Everbody can download it from [http://www.iArbo.nl] OR [http://www.ohs-apps.com]
    Maybe it is possible to translate the thesis with [http://translate.google.com]

    In this thesis have done (1) an exploration of the use of ohs apps under the OHS professionals in the Netherlands and the effect on their work (614 ohs professionals filled in my survey). (2) an exploration of the available apps in the field of Oh&s (3) comparison the use of apps clinical medical field and the ohs field: what are risks OR opportunities…
    During the writing of the thesis I also found extended labtests of smartphone types in different combinations with different noise apps!! In my thesis you Will find the references.
    I have als done à practical comparison test with CO2 sensor (gadget for approx $150) versus à TSI QTRAK (approx. $2000)

    It is definitly opening an new research field and (i believe) an necessity for ohs professionals to learn about the apps risks and possibilties. It has an potential for empowering employees and ohs professionals.
    Questions? hoevers@gmail.com
    With Fr. Grtz Ronald Hoevers

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    • AUTHOR COMMENT April 11, 2014 at 3:07 pm ET  -   Chuck Kardous

      Thank you for sharing your thoughts and your thesis. We will get in touch if we have any questions.

      Link to this comment

  4. April 10, 2014 at 3:18 pm ET  -   brettmd (@BrettSnodgrass1)

    Healthcare Apps Doctors

    Thank you.

    Link to this comment

  5. April 14, 2014 at 12:53 am ET  -   Simon

    This is really a comprehensive article that I have gone through at the moment. I believe that accuracy of the apps depend upon the skill and approach of the mobile app developer and if the app is customized it also depend upon the way things and details explained by the people who need it.

    Link to this comment

    • AUTHOR COMMENT April 15, 2014 at 12:44 pm ET  -   Chuck Kardous

      Thank you for your comment, we agree that the accuracy of some apps highly correlates to the skill and approach of the app developer. Some of these apps have been developed by highly-skilled engineers and programmers who have a great understanding of the principles of acoustics, sound measurement, and applicable noise standards.

      Link to this comment

  6. April 18, 2014 at 4:08 pm ET  -   Carel Ostendorf

    Thanks for your interesting article. In July 2013 I have tested several free apps myself mainly to see how my app SafeNoise was doing compared to other free apps. You can find an article about my test on

    [http://www.geluidnieuws.nl/2013/jul2013/app.html] (only in Dutch).

    In my test I have used 5 samples:
    - pink noise with a sound level of 80 and 100 dB(A)
    - pure tones of 80 Hz (81 dB(A) and 4 kHz (93 dB(A)
    - rockmusic 93 dB(A)
    The setup was straight forward using a stage floor monitor (35 Hz to 16 kHz), a PA amplifier and a laptop with the sound samples. The smartphone and the reference microphone were located close to each other about 1.5 mtr distance from the speaker and pointed directly to the speaker. Due to the short distance between speaker and microphones, there was no influence of the room acoustics (about 65 m3, RTs between 0,5 and 0,2).
    I also checked the influence of the position of the smartphone and the reference microphone (figures 3 and 4 in my article).

    The iOs apps turned out to be better than the Windows or Android apps. Some iOs apps performed within 2 dB(A) of the reference soundlevel meter (MusicSafeCheck and SafeNoise). Did you test those apps as well? If so, how did they do?

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    • AUTHOR COMMENT April 21, 2014 at 10:56 am ET  -   Chuck Kardous

      Thank you for sharing your article, it would be greatly beneficial to the readers of this blog if there is an English translation or if you plan to publish it in a peer-reviewed journal. We examined hundreds of apps but selected 10 iOS apps and 4 Android apps for additional testing. None of the Windows-based apps met our selection criteria. See our journal article for our selection criteria of the apps we tested and their performance.

      Link to this comment

  7. April 20, 2014 at 4:49 pm ET  -   Harold Forester

    I was surprised to find that the microphones used in the Apple phones have a fairly flat frequency response, as I thought that all cell phone mics were intended to capture speech and therefore had poor responses at both the low and high end of the frequency spectrum. That means that mics used in Android devices, even when the apps have been properly calibrated, can give a fairly accurate sound level for sounds in the speech frequency range (500 Hz to 2000 Hz range), but can give very inaccurate results when recording other sounds with low and high frequency content, such as from music and diesel engines.

    Link to this comment

    • AUTHOR COMMENT April 21, 2014 at 10:55 am ET  -   Chuck Kardous

      The microphones themselves exhibit a good flat frequency response up to around 10-12 kHz depending on the type of MEMS microphone used in each device, the smartphone manufacturers introduce speech and noise cancelling filters into the system for normal communication needs. However, starting with iOS 6, Apple allowed developers to bypass such filters. Android developers must still work around such filters during the development of their apps.

      As far as microphones used in Android devices, they’re usually similar to those found in Apple devices, almost all smartphone manufacturers rely on few suppliers of MEMS microphones. The difference in performance and accuracy across devices and platforms are not necessarily related to the microphones but rather the set of software and drivers that handle and process the audio signal. Apple offers its developers access to their digital audio infrastructure, called Core Audio, which is tightly integrated with the iOS. No such infrastructure exists for other platforms such as Android and Windows as they continue to rely on third-party drivers and that can introduce latency and affect the performance of the apps.

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  8. April 23, 2014 at 8:30 am ET  -   Alice Thompson

    Thanks for informative post.

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  9. April 25, 2014 at 10:52 am ET  -   Michiel van Eeden

    Thanks for this investigation.
    Steady broadband noise test signal: the test should be extended with offering bursts (in free field!) and signals with high (but realistic) crest factors.
    The test should also be extend with performance at different temperatures for example. Some other factor maybe added, for example if it has a fair high frequency response (think about compressed air noise).

    Then, if you clearly inform the user about all limitations, selected apps could be very well useful. Of course no one should expect the “full performace” of such apps. But it will be used by a large audience with little knowledge about the subject; then its important that they know were it goes wrong.

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    • AUTHOR COMMENT April 25, 2014 at 3:05 pm ET  -   Chuck Kardous

      Thank you for your feedback, we will take your input into consideration if we decide to expand our study.

      Link to this comment

  10. May 8, 2014 at 5:05 am ET  -   schalke trikot

    I cannot thank you enough for the blog article.Really looking forward to read more. Really Cool.
    schalke trikot

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  11. May 14, 2014 at 3:33 am ET  -   nancy

    Thanks for sharing this blog..

    Link to this comment

  12. May 25, 2014 at 5:45 am ET  -   Dan

    OK, So I’m far from an intellectual and honestly just barley graduated High School. Most of what’s said here is Greek To Me. I work in a night club doing as best as I can for My Family with what I have. I’ve noticed several of the older people there who have admitted to being in clubs for a long time have difficulties in hearing. What I’m trying to do is find a device / app that I can turn or / activate that can give me a”DECENT” reading and tell me if I could be wearing hearing protection or not ? I understand that some people or business’s are not allowed to say choose this one over this one, but as a person who DOES NOT want to lose his hearing and can not quit right now, could someone PLEASE put in PLAIN ENGLISH the good, the bad or the indifferent. I have an older iphone 4 and really want to know. Thank You. Dan

    Link to this comment

    • AUTHOR COMMENT May 29, 2014 at 3:38 pm ET  -   Chuck Kardous

      We appreciate your comment and sincere request. Please note that NIOSH does not recommend nor endorse a particular commercial product and also note that this was a pilot study so there may be other apps out there that may be as accurate as the ones we tested. The results of our study showed that the SPLnFFT app from Fabien Lefebvre and SoundMeter app from Faber Acoustical had the best accuracy, followed by Noise Hunter and NoiSee. All of these apps are available through the iTunes app store. Take a look at the description and screen layout of each and choose an app that you feel most comfortable using. Any of these apps should be adequate to do the job (The apps pricing range from $0.99 for NoiSee to $19.99/$99.99 for SoundMeter).

      The most important thing is to get 3-5 readouts over different periods of times so you can get a better understanding of the noise environment at your club and find out what the overall average noise levels. To make sense of the noise level readouts you get from a particular app, note that the NIOSH recommended exposure over an 8-hour workday is 85 decibels, A-weighted (dBA), and for every 3-dB increase in that level, you cut exposure time in half, so if your reading is 88 dBA, , you should only be exposed to that level of noise for up to 4 hours (per day), at 91 dBA, exposure time is cut to 2 hours, and so on. See Table 1-1 in this document http://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf and try to match the noise level readout to the recommended exposure duration. Remember, these apps are only meant to give you a rough idea about your environment, they do not replace the need for a professional noise assessment. But if your readouts exceed our recommended limit of 85 dBA on a consistent basis, then it might be worthwhile to share that information with the club management and see if they can address it. There are a variety of solutions available to an employer, from reducing and controlling the noise levels, to administrative controls such as limiting time spent in the area with the excessive noise and taking breaks, or if those are not possible, offering hearing protection. There are many different kinds of hearing protectors available these days, such as the “musicians’ earplugs” that attenuate noise uniformly across all frequencies without distorting speech and music. Based on your description of your job, the musicians’ type of protectors would seem to be ideal for your situation.

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  13. May 28, 2014 at 7:37 am ET  -   Mukesh Joshi

    Very informative article. I run Techogeek which is based on Smartphone apps and reviews and i will definately write something for you

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  14. June 8, 2014 at 3:09 am ET  -   Vishnu

    This article Seems to be nice. It is really informative as well as well written. Also looking forward to read another article like this. Once again thanking you for such an article..

    Link to this comment

  15. June 16, 2014 at 8:12 pm ET  -   Super Vid

    I believe that accuracy of the apps depend upon the skill and approach of the mobile app developer and if the app is customized it also depend upon the way things and details explained by the people who need it.
    Super

    Link to this comment

  16. July 10, 2014 at 3:20 am ET  -   Aspiratech

    Great post, got to know many things about mobile apps review
    thanks for sharing it

    thanks and regards

    Link to this comment

  17. July 15, 2014 at 8:36 am ET  -   Zhihan Ng

    Chanced upon this study back in May and proceed to ‘mix and match’ the setup with the SoundMeter app coupled with the i436 and used it for area noise measurements at some workplaces in Singapore. The results, when compared with a calibrated SLM type II are pretty close.

    Link to this comment

    • AUTHOR COMMENT July 15, 2014 at 2:36 pm ET  -   Chuck Kardous

      Thank you for your comment, please share with our readers some of your findings. We are in the process of conducting a study with several external microphones.

      Link to this comment

  18. July 15, 2014 at 10:28 am ET  -   Mark

    Thanks for the great post.Very informative in relation to the future of voice commands. Thanks for a good blog.

    Link to this comment

  19. July 16, 2014 at 2:37 am ET  -   Salesforce Training

    Thanks for sharing the information

    Link to this comment

  20. July 16, 2014 at 8:03 am ET  -   J.Garcia

    Thank you

    We are grateful to read articles like that. I like talking mobile design.

    regards

    Link to this comment

  21. July 16, 2014 at 4:21 pm ET  -   Mohsin

    interesting information. The highest rated app for sound measurement are there in market, but there is still room for improvement. 30 iPad sound measurement apps reviewed after extensive testing here : http://www.safetyawakenings.com/safety-app-of-the-week-42/. thank you for the nice information.

    Link to this comment

  22. July 18, 2014 at 9:57 am ET  -   Peter

    It is incredible that a smartphone can do so much these days. I believe that a smartphone will replace the laptop one day

    Peter Gajetto

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  23. July 19, 2014 at 12:50 am ET  -   Ethnic Food

    Spectacular post. nicely written

    Link to this comment

  24. July 24, 2014 at 4:38 pm ET  -   Pierre Aumond

    Thanks for your interesting article. However I would like to understand something. 1.Why you don’t speak about the hudge variability that’s posible to see in the figure 2 ?
    2.The App was more accurate at low level or High Level ?

    By the way, that a good investigation,

    Best regards.

    Link to this comment

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