Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level (20 µPa, which is usually considered the threshold of human hearing at 1 kHz). I have earlier used several different decibel meters to measure sound levels (both commercial and DIY circuits).
It would be quite nice if I could do the same measurement with my smart phone or tablet. Basically for sound level measurement all you need is a microphone, some instrument to show the signal level on logarithmic scale and some way to calibrate the system. A modern smart phone has a suitable microphone and means to display the measurement on logarithmic scale. All I then need is to get a suitable application and some way to do the calibration, and I should have a portable dB meter always with me.
For making the measurements with Android I found two promising free apps: Sound Meter and Sound Meter PRO. The Play store has also many other apps for the same applications, but at first tests those seemed to be the best of ones I tested.
Sound Meter PRO is a free Android app to measure sound level. Sound Meter PRO uses your Android’s microphone to measure levels of noise or sound pressure levels and displays measured data in dB (decibels) with reference to generally known noise (provided by American Academy of Audiology) or displays the noise data on easy to read graph for the last 30 seconds of app use. Sound Meter PRO information page says that it is calibrated to be accurate in +-2.5 dB range of actual noise level and is claims to be probably by far the most accurate sound meter on Google play. On my Samsung S4 phone the accuracy claim seems to hold well against a commercial dB meter. The app notes that the microphones in Android devices are made to record human voice, therefore the maximum noise is limited and very loud sounds cannot be recognized (in most cases above 100dB).
Sound Meter is a simple to use free Android app for SPL measurement. SPL(sound pressure level) meter app uses your built-in microphone to measure noise volume in decibels(db), and shows a reference. The app descriptions says that the built-in microphones on many phones are aligned to human voice (300-3400Hz, 40-60dB), so there can be issues related to frequency response and maximum sound level that can be measured. I tested the app and found that it works well. There is even an option to do calibration (put phone next to some known accurate dB meter and do calibration). On my Samsung S4 mini phone the results were pretty close to dB meter without any calibration! I recommend this Sound Meter app.
Both Sound Meter and Sound Meter PRO apps worked well for me. You can use either one of them if you need to do some dB measurements (or you can install both of them like I did). The measured results are expected to be within few dB of the real value with those apps (and more accurate if you can calibrate them against some known meter or signal source). Happy audio measurements with your smart phone.
If you want to do also other measurements to sound than just the volume, check also my older posting Use your smartphone or tablet as signal analyzer.
19 Comments
Yorkor Ban says:
Needed for testing purpose
Yorkor Ban says:
The Sound Meter and Sound Meter PRO are good instruments worth having for noise measurement.
Yorkor Ban says:
I am a specialist in Noise measurements and studies in communities and work places. I therefore need the Sound Meter and Sound Meter PRO for quick data acquisition, verification and validation.
They will help me achieve a lot in my profession.
jay singh says:
hi, can SPL level measure up to 160dbl.
this is through an andriod phone.
Tomi Engdahl says:
I don’t think it can measurement range with built-in microphone on smart phone is typically limited to maximum 120-130 dB range.
Richie says:
I have both of them. I tried another one along with the two you tested and the other one was 10dB over.
Sound Meter & Sound Meter Pro are the best.
Colton #SoundqubedBoy says:
I hit a 154.7db on expensive db meters with my 2 hdc415s on 7k. This thing says I hit 110… Lol ok
Tanaji Gajare says:
Very nice blog post.
I had one question that is there any windows app for noise level measuring? i tried looking for it but no luck.
btw we have also written blog on this subject have a look at it. http://www.ppsthane.com/blog/sound-level-measuring-using-smartphones
Tomi Engdahl says:
This looks promising:
How to Use a PC As a DB Meter
https://www.techwalla.com/articles/how-to-use-a-pc-as-a-db-meter
https://www.microsoft.com/en-us/store/p/decibel-meter/9wzdncrdf7lz
Tomi Engdahl says:
This app works, but it seemed to give different readings (almost 10 dB difference) than my Android phone
https://www.microsoft.com/en-us/store/p/decibel-meter/9wzdncrdf7lz
I belive the readings with Android phone that seemed to be quite close to real ones (checked against dB meter device).
Daniel Harrell says:
A guy on YouTube is into car audio he had a phone that measured up into the 150′s, he didn’t have a Bluetooth external meter he was using his phone only so their is a device out their that can do this he won’t comment back on identifying the phone but it is possible
Tomi Engdahl says:
Evaluation of smartphone sound measurement applications
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4659422/
This study reports on the accuracy of smartphone sound measurement applications (apps) and whether they can be appropriately employed for occupational noise measurements. A representative sample of smartphones and tablets on various platforms were acquired, more than 130 iOS apps were evaluated but only 10 apps met our selection criteria. Only 4 out of 62 Android apps were tested. The results showed two apps with mean differences of 0.07 dB (unweighted) and −0.52 dB (A-weighted) from the reference values. Two other apps had mean differences within ± 2 dB. The study suggests that certain apps may be appropriate for use in occupational noise measurements.
Occupational and general purpose sound level measurements are conducted using type 1 or type 2 sound measurement instruments that must meet the requirements of ANSI S1.4-1983 (R2007), Specifications for Sound Level Meters [ANSI, 1983 (R2007)]. ANSI S1.4 states the following: “The expected total allowable error for a sound level meter measuring steady broadband noise in a reverberant sound field is approximately ± 1.5 dB for a type 1 instrument and ± 2.3 dB for a type 2 instrument.” For compliance with occupational and environmental noise requirements, standards and regulations in the United States require that instruments meet ANSI type 2 specifications. The Occupational Safety and Health Administration (OSHA) noise standard (29 CFR 1910.95) considers type 2 instruments to have an accuracy of ± 2 dBA.
This paper describes a pilot study to assess the functionality and accuracy of smartphone sound measurement apps, examine the variability of device hardware on the accuracy of the measurements, and determine whether these apps can be relied on to conduct participatory noise monitoring studies in the workplace.
A total of 62 Android apps were examined and downloaded from the Google Play store but only 4 apps (SPL Meter by AudioControl, deciBel Pro by BSB Mobile Solutions, dB Sound Meter by Darren Gates, and Noise Meter by JINASYS) partially met our selection criteria.
There were only two non-commercial apps available on both the iOS and Android platforms: Noise Exposure/Buller published by the Swedish Work Environment Authority, and NoiseWatch published by the European Environment Agency.
Almost all smartphone manufacturers use microelectromechanical systems (MEMS) microphones in their devices. MEMS microphones typically have a sensitivity between 5 and 17.8 mV/Pa and can capture signals as low as 30 dB SPL and as high as 120 to 130 dB SPL (signal-to-noise ratio >60 dB). MEMS microphones also have a flat frequency response similar to ceramic and condenser microphones used in type 2 noise dosimeters. With the introduction of the iOS 6 operating system in late 2012, Apple allowed developers to bypass the high-pass filter that degraded the quality of acoustical measurements on older iPhones. This development also allows users of Apple smart-phones to connect external microphones through the headset input jack. External microphones such as the MicW i436 (Beijing, China) Omni-directional measurement microphone comply with IEC 61672 class 2 sound level meter standard.
The Android-based apps did not have features and functionality similar to the iOS apps. This is likely due to the development ecosystem of the Android marketplace and users’ expectations for free or low priced apps.
The limited testing showed a wide variance between the same app measurements on different devices. This can likely be attributed to the fact that Android devices are built by several different manufacturers and that there is a lack of conformity for using similar microphones and other audio components in their devices.
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, the overall accuracy of the sound apps, bad or corrupted data, and mechanisms for storing and accessing such data.
Conclusions
This study showed that certain sound measurement apps for Apple smartphones and tablets may be considered accurate and reliable to be used to assess occupational noise exposures. Android and Windows developers do not offer apps that meet the functionality needed for occupational noise assessments.
Tomi Engdahl says:
Evaluation of smartphone sound measurement applications (apps) using external microphones – A follow-up Study
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5102154/
This follow-up study examines the accuracy of selected smartphone sound measurement applications (apps) using external calibrated microphones. The initial study examined 192 apps on the iOS and Android platforms and found four iOS apps with mean differences of ±2 dB of a reference sound level measurement system. This study evaluated the same four apps using external microphones. The results showed measurements within ±1 dB of the reference. This study suggests that using external calibrated microphones greatly improves the overall accuracy and precision of smartphone sound measurements, and removes much of the variability and limitations associated with the built-in smartphone microphones.
The National Institute for Occupational Safety and Health (NIOSH) estimates that more than 22 million people in the United States are exposed to noise levels in excess of 85 A-weighted decibels (dBA) at their place of work. The World Health Organization (WHO) estimates that more than 5% of the work population – 360 million people – have disabling hearing loss
Professional sound level meters (SLMs) must comply with national and international standards such as American National Standards Institute (ANSI) S1.4-1983 (R2007), Specifications for Sound Level Meters (ANSI, 1983 (R2007)) and International Electrotechnical Commission (IEC) 61672-1, Sound Level Meters – Part 1: Specifications (IEC, 2013). Both standards specify a host of acoustical and electrical tests with indicated tolerance limits and measurement uncertainties that are specified in decibels over a wide frequency range (typically from 10 Hz – 20 kHz). Such tests must account for level linearity, directionality, time and frequency-weighting responses, tonebursts, radio frequency interference, and atmospheric and environmental conditions. The standards also specify that these tests shall be made on the complete instrument, including the microphone and pre-amplifier. As of today, no smartphone or smartphone-based app has met the requirements of IEC or ANSI standards.
In 2014, we examined 192 sound measurement apps on the iOS and Android platforms and found only four iOS apps that had the means of their differences with a type 1 sound level meter to be within ± 2 dB over a 65 – 95 dB SPL test range. Overall, none of the Android-based apps met our initial test criteria, mainly because the Android marketplace is fragmented among many manufacturers with different requirements for parts and lack of uniform audio integration of software and hardware across the different devices
However, a major weakness remains the micro-electro-mechanical-system (MEMS) built-in microphone used in smartphones. Advances in MEMS microphone design and technology show that these microphones now rival the best electret and condenser microphones used in current sound measurement instruments in terms of frequency response, power requirements, and environmental/electromagnetic specifications. MEMS microphones continue to have certain limitations because of their miniature size and circuit board placement, which affect their dynamic range and signal-to-noise ratio response
Another major constraint presented by the built-in microphones is the lack of access and inability to perform periodic or pre-measurement calibration. Several apps have a feature that allows users to attach an external microphone to the iOS devices headset jack input. Few “audio measurement” external microphones are available commercially that use the 4 contact, Tip-Ring1-Ring2-Sleeve (TRRS) configuration for use with most smartphone headset jacks. Two external microphones with similar specifications were selected for this study, an inexpensive Dayton Audio iMM-6 (Springboro, OH) microphone and the more expensive MicW i436 (Beijing, China) that is reported by the manufacturer to be in compliance with IEC 61672-1 Class 2 specification. Both microphones use electret-condenser capsules and are omnidirectional.
Results
The results of testing the fixed effects of the smartphones apps showed that there was no evidence of differences between apps
Also, there was no evidence that the measurements of the four apps differed from those made by the reference system; the least squares means of differences did not differ significantly from zero, as indicated by the fact that all of the 95% confidence intervals for the estimates contained zero
Discussion
The manufacturer, MicW, claims that the i436 microphone complies with IEC 61672 class 2 sound level meter standard. It is important to note that IEC-61672 provides specifications for sound level meters as an entire system (microphone, signal processor, and a display device) whether it is a self-contained, hand-held instrument, or a combination of the above, not just the microphones.
Overall, all four apps performed well using both sets of external microphones. It is interesting to note that the medians of the differences for the iMM-6 microphones are slightly higher than those measurements made with the i436 microphones. This means that the measurements taken using the iMM-6 microphones tend to be slightly lower (~ 0.1 – 0.2 dB) than those made with the i436 microphones. This is possibly due to differences in the frequency responses and the nominal sensitivities of both microphones.
Since the acquisition of acoustical calibrators may be prohibitively expensive for some users, some app developers have implemented pre-defined profiles for external microphones by incorporating known sensitivity values that the user can select, and the app calculations will be adjusted accordingly based on those sensitivity values. As more external microphones become available commercially, we expect developers to start including those pre-defined microphone profiles into their apps or make them available for uploading on their sites. Although pre-defined profiles may solve the need for calibration on a short term basis, microphone performance could degrade over time, especially if dropped or repeatedly exposed to extreme environmental conditions. Professional instruments are typically calibrated before and after every measurement and are also sent out for calibration at accredited laboratories. Because this practice may not be feasible with smartphones, it should not be assumed that pre-defined profiles will continue to work with a specific microphone over a long period of time. Routine checks with an acoustic calibrator before and after each measurement session will remain the preferred method for obtaining accurate readings.
Although not examined in this study, the use of external calibrated microphones may lead to similar findings when used with Android-based apps. One of the main issues encountered with Android-based apps in the earlier study was the fragmented marketplace for hardware devices and lack of uniformity of audio integration between the tens of different manufacturers. The selection and use of an external, calibrated microphone removes many such obstacles.
Tomi Engdahl says:
So How Accurate Are These Smartphone Sound Measurement Apps?
https://blogs.cdc.gov/niosh-science-blog/2014/04/09/sound-apps/
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
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.
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.
November 2016 Update: NIOSH researchers have just published a follow-up study: Evaluation of smartphone sound measurement applications (apps) using external microphones to examine the performance of sound measurement apps using external microphones. The study showed sound level measurements to be within ±1 dB of the reference system using the same test setup and apps from the initial study.
Tomi Engdahl says:
The Tachometer Inside Your Smartphone
https://hackaday.com/2018/02/08/the-tachometer-inside-your-smartphone/
It’s the latest in instrumentation for the well-appointed shop — an acoustically coupled fast Fourier transform tachometer. Sounds expensive, but it’s really just using a smartphone spectrum analyzer app to indirectly measure tool speeds. And it looks like it could be incredibly handy.
https://www.youtube.com/watch?v=xutm6oMTBw8
Tomi Engdahl says:
Smartphone decibel meter apps to measure noise levels
https://www.healthyhearing.com/report/47805-The-best-phone-apps-to-measure-noise-levels
You’re bringing the grandchildren to see your favorite professional sports team take on the league leaders. Will the roar of the crowd be enough to warrant wearing ear protection? Or maybe you’ve hired a local band to play outside at your daughter’s graduation party. Is the music too loud for your guests and the neighbors?
Tomi Engdahl says:
iOS app:
Free Sound Level Meter App from CDC’s National Institute for Occupational Safety and Health
https://www.noisyplanet.nidcd.nih.gov/have-you-heard/cdc-niosh-app
Do you work in or near a noisy environment, such as a construction site, a popular restaurant, or a concert or sports venue? Ever wonder how loud the noise really is and if it could be damaging your hearing? There’s an app for that!
The National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control and Prevention (CDC), developed the NIOSH Sound Level Meter (SLM) app for iOS devices to help promote better hearing health and prevention efforts. You can download the free app
on iTunes.
NIOSH estimates that 22 million workers in the United States are exposed to hazardous noise levels each year. The SLM app can help you prevent permanent hearing loss caused by noise—a problem that can occur immediately or over time.
For example, NIOSH SLM reports the sound level in different weighted decibels, including A-weighted decibels, which can give you a good idea of the level of sound that could harm your hearing.
NIOSH Sound Level Meter App
https://www.cdc.gov/niosh/topics/noise/app.html
NIOSH Sound Level Meter App
Close-up of downloaded Sound app.
The NIOSH Sound Level Meter (SLM) app combines the best features of professional sound levels meters and noise dosimeters into a simple, easy-to-use package. The app was developed to help workers make informed decisions about their noise environment and promote better hearing health and prevention efforts.
Key Features
Developed by experienced acoustics engineers and hearing loss experts.
Tested and validated (accuracy ± 2 dBA) according to standards in a reverberant chamber at the NIOSH acoustics lab – the only proper method to validate accuracy.
Meets Type 2 requirements of IEC 61672:3 SLM standard when used w/ external microphone.
Provides the most relevant metrics found in professional sound instruments today. Averages such as LAeq and TWA, Max and Peak Levels, Noise Dose and Projected Dose according to NIOSH and OSHA standards, and all three major weighting networks (A, C, and Z).
Capability to calibrate either internal or external microphone. Reporting and Sharing data.
Up-to-date informational screens on what noises are considered hazardous, how to conduct a noise measurement, how to properly select a hearing protector, and guidelines for preventing hearing loss.
Technical support available directly from NIOSH hearing experts.
Tomi Engdahl says:
NIOSH Sound Level Meter app for iOS devices
https://www.youtube.com/watch?v=ZUoeDlYOAIQ
The NIOSH Sound Level Meter (SLM) app for iOS devices can be used by safety and health professionals and industrial hygienists to assess risks, similar to how they would use a professional sound level meter, and by workers to make informed decisions about the potential hazards to their hearing in the workplace. The app allows the user to acquire and display real-time noise exposure data and help promote better hearing health and better prevention efforts. Read and comment about the app on our science blog:
https://blogs.cdc.gov/niosh-science-blog/2017/01/17/slm-app/
Tomi Engdahl says:
NIOSH Mobile Applications (Apps)
https://www.cdc.gov/niosh/pubs/apps/default.html
NIOSH Sound Level Meter
https://apps.apple.com/us/app/niosh-sound-level-meter/id1096545820