Sound Level Analyzer PRO


"Sound Level Analyzer PRO" is an integrated sound measurement app with sound level measurement and powerful sound analysis tools.

It can display automatically the instantaneous sound level such as environmental noise, specific sound sources, live sounds in real-time.

"Sound Level Analyzer PRO" is a professional-grade sound level measurement app further evolved from “Sound Level Analyzer".

In addition, this app has advanced sound analysis functions that can perform "Power Spectrum Analyzer", "Time Course graph", and "Statistical Analysis (Histogram, Percentile Level)".

It can be used to analyze characteristics and trends of occurrence for the noise/sound source.

The latest version supports iOS 17 and improves stability and performance. Changed the display position of the occurrence time and the maximum level in "Display Max" at P.S. mode.

slapro_main slapro_ps_all
slapro_tc slapro_sa_hist

The WHO has proven direct links between noise and health risks; tinnitus, sleep disturbance, stress, cognitive impairment, heart diseases and annoyance in general. Please check your environmental noise for your wellness.

"Sound Level Analyzer" has received the highest rating as a sound level meter app in the research paper of acoustic academic journal "Applied Acoustics". (Paper: ”Testing the accuracy of smartphones and sound level meter applications for measuring environmental noise”, Enda Murphy, Eoin A. King ; Applied Acoustics 106(2016)16-22.)

Please click on the link below to access "Sound Level Analyzer PRO" product page in App StoreTM.

It will move to another site, download from Apple Store

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Products Information

Version: 6.0.1
Release date: October 2, 2023. UTC
Size: 0.7 MB
Category: Utilities, Life style
Compatibility: Compatible with iPhone. Requires iOS 16.6 or later.
Status: Now distributing.


"Sound Level Analyzer PRO" has the following features:

Sound level measurement (dB): Main (Leq)

- Leq (equivalent sound level), Min (minimum value), Max (maximum value), Avg (time average equivalent sound level)

- Frequency weighting correction characteristics: A (for noise level meter), C (for sound level measurement), Z (no correction)

- Time weighting characteristics : Fast = 0.125 sec, Slow = 1.0 sec

- Display Range: 0 - 130 dB

Power Spectrum (P.S): View of frequency spectrum analysis

- Spectrum analyzer function: FFT analysis, 1/3-octave band response analysis.

- 1/3-octave band center frequency: 25, 31.5, 40, 50, 63, 80, 100, 125, 160, 200,
250, 315, 400, 500, 630, 800, 1k, 1.25k, 1.6k, 2k, 2.5k, 3.15k, 4k, 5k, 6.3k, 8k, 10k, 12.5k, 16k, 20k (Hz)

- FFT frequency range settings: 100Hz - 20kHz (FFT All) / 100Hz - 3kHz / 3k - 6kHz

- Measured value display function in 1/3 oct band response analysis. (OctVal)

- Power spectrum display function at the time of occurrence of Max. (Display Max)

Time Course (T.C): View of time-history of the sound level.(graphical representation after measuring completion.)

- Time-domain fluctuation level display function: up to 8 hours linked on a timer.)

Statistical Analysis (S.A) : Statistical analysis of sound level at A-weighting and Fast. (analysis display after measuring completion.)

- Histogram: Displays all detected sound level distribution as a percentage.

- Percentile level (LN:dB): Display the levels of L05 / L10 / L50 / L90 / L95 on the percentile level graph.

Calibration function: level correction value settings, -20 to +20dB / 0.1dB unit
Measurement timer function (Timer): 1 minute / 5 minutes / 10 minutes / 15 minutes / 20 minutes / 30 minutes / 1 - 8 hours (1 hour unit)
Snapshot (Snap): Save measurement display with time stamp to Photos.


"Sound Level Analyzer PRO" can be used for various applications as follows:

Live Sound
Environmental noise measurement
Setting and Tuning of Audio system
Installation of Audio equipments
Installation of Car audio equipments
Architectural acoustics
Device management

In addition, the followings are examples of the magnitude of the sound level in the measurement of environmental noise.

130dB: Engine sound of Airplane
110dB: Horn of Car
100dB: Noise of passing train
90dB: In loud factory
80dB: In the train, Vacuum cleaner
70dB: Noisy office, Noisy street
60dB: Quiet Car, Normal conversation
50dB: Quiet office
40dB: In the library, Quiet residential area
30dB: Outskirts of midnight, Whisper
20dB: Sounds of rubbing leaves

Note: The standard noise measurement range is 30-130dBA, and the measured value (Leq) is about 30dBA in a quiet room of the household. Due to the presence of background noise, noise levels are never measured at 0dBA even in very quiet environments.

Important initial settings

In order for this app to work properly, it is necessary to make the following initial settings related to the iOS system.

Microphone access permission setting

At the initial startup after installing the app, the iOS system asks for permission to access the built-in microphone. In this case, you need to enable access to "Microphone".

If you have not enabled this setting, this app can not work by privacy restrictions of the iOS system. Please enable the access permission on the iOS setting, "Settings > Privacy & Security > Microphone".


Photos access permission setting

When the first time you save an image data with Snapshot, the iOS system asks for permission to access the "Photos" library. In this case, you need to enable access to "Photos".

If you have not enabled this setting, this app can not work by privacy restrictions of the iOS system. Please enable the access permission on the iOS setting, "Settings > Privacy & Security > Photos".


Operation Mode

"Sound Level Analyzer PRO" has four types of measurement analysis modes. By tapping on each mode button, you can select one of the modes and display it. The function of each mode is as follows.


Measurement analysis mode

MAIN (Leq): Sound level measurement (dB)
P.S: Power Spectrum
T.C: Time Course (graphical representation after measuring completion.)
S.A: Statistical Analysis (analysis display after measuring completion.)

"MAIN (Leq) mode" and "P.S mode" are also switched during measurement operation.

"T.C mode" and "S.A mode" can be selected and displayed only after the sound level measurement is completed.

The access permission to the microphone will be confirmed from the iOS system at the first boot-up. Be sure to enable access to the microphone.

In addition, it will start up in MAIN (Leq) mode at the first boot-up.

MAIN (Leq): Sound Level Measurement

"MAIN (Leq) mode" makes the sound level measurement in general. In this case, by applying the appropriate Frequency Correction, Time Correction, and Level Correction, you can be the best sound level measurement.

Tap the play button to start the sound level measurement, and it then pause by tapping it again.

slapro_main slapro_main_c_slow

Sound level measurements are displayed measured values​ of Equivalent continuous sound level (Leq), minimum value (Min), maximum value (Max) and Time average equivalent sound level (Avg) in dB units. The Leq is also displayed as a color bar graph.

Leq: Equivalent sound level - Instantaneous value of sound level (Noise level) (dB)
Avg: Time average equivalent sound level - Time moving average value (dB)
Min: Minimum sound level - Minimum value within the measurement time (dB)
Max: Maximum sound level - Maximum value within the measurement time (dB)

It also displays a short-term time variability graph at the same time. This graph shows the sound level fluctuations for the past 20 seconds. The graph shows the Leq level (white bar), the Avg level (green line), and the moving average level for 10 seconds (orange line).

It can be measured as parameters, Time weighting correction, Frequency weighting correction, and Level calibration, to set as follows:

Time weighting correction

It specifies the time constant of calculating the sound level. Please set in accordance with the occurrence tendency and type of sound source.

FAST: 0.125 sec (Default)
SLOW: 1.0 sec

Frequency weighting correction

It is a weighting filter that limits the frequency band of the input signal. Please set according to the measurement applications.

A: A correction - Noise measurement by general audibility correction (Default)
C: C correction - Sound pressure level measurement for wideband sounds and music
Z: Non correction

Level Calibration

You can specify the reference level in the offset range. Tap the calibration value window in Info view, the input keyboard will appear. If you have the standard sound level meter, please use it to adjust the reference level.

Offset ranges: -20dB to +20dB in 0.1dB unit

P.S: Power Spectrum

"P.S mode" displays frequency spectrum analysis in real time. Measurement is displayed by 1/3 octave band response and FFT analysis.

The 1/3 octave band analysis displays the signal response of the input signal's frequency spectrum in 1/3 octave and 24 band (100 Hz to 20 kHz).

FFT analysis displays the FFT spectrum by Fast Fourier transform. You can also select the FFT frequency range with high audibility.

FFT frequency range

All: 100Hz - 20kHz
Scope 1: 100Hz - 3kHz
Scope 2: 3kHz - 6kHz
slapro_ps_all slapro_ps_sc1 slapro_ps_sc2

Tap "OctVal" button, it can display the measured values for each band of 1/3 octave band analysis in real-time.


Tap "Display Max" button, it can display the frequency spectrum characteristics at the moment when the maximum sound level "Max" has occurred. At this time, you can see the measured values for each frequency band by tapping "OctVal" button.

slapro_ps_all_max slapro_ps_vmax_octval

T.C: Time Course

"T.C. mode" displays the time course graph of the sound level.

In conjunction with the timer, fluctuation data of the sound level up to 8 hours is recorded, and the time course graph can be displayed in all the measurement time. "T.C. mode" can be selected only after measuring completion.

The time course graph is displayed with time as Y axis and sound level (dB) as X axis, and it can be displayed by scrolling. The moving average level can also be displayed.

In addition, you can select graph display in 1 hour unit with the buttons from "0" to "7" at the bottom.


S.A: Statistical Analysis

"S.A. mode" displays the statistical analysis focusing on sound level fluctuation.

In conjunction with the timer, fluctuation data of the sound level up to 8 hours is recorded, Histogram and Percentile level can be displayed as a sound level statistical analysis on all measurement time. "S.A. mode" can be selected only after measuring completion.


It displays the noise level distribution showing the occurrence frequency of sound level as a percentage. It can intuitively grasp which sound level occurred frequently in all measurement time. It may be shown the occurrence of steady noise and the distribution trend of the noise floor. The X axis is the sound level (dB), and the Y axis is the incidence of each sound level. In addition, the cumulative relative frequency distribution curve is also displayed.


Percentile level

It displays the percentile level LN (L5, L10, L50, L90, L95), and the cumulative relative frequency distribution curve.

In this statistical analysis, when the total time exceeding a certain level corresponds to N% of the measured time in the fluctuating noise within the measured time, the noise level is expressed as N% hourly noise level (LN). The percentile level can be used to evaluate the noise environment where the noise level is random or it fluctuates dramatically.


Also, in the sound statistical analysis, the following measurement time is required. Please note that the required measurement time varies depending on the timer setting.

Timer setting and Required measurement time

1 min: 10 sec or more
5 min: 30 sec or more
10 min over: 60 sec or more

Snap Shot

Tap "Snap" button, you can capture the measured image to Photos. It is possible in all modes.



Tap "Setting" button to display the timer settings in the Info view. The setting time can be selected by the picker from 1 minute to a maximum of 8 hours. To return to the previous view by tapping "Close" button.

Timer period: 1 min / 5 min / 10 min / 15 min / 20 min / 30 min / 1 - 8 hour(1 hour unit)

Information view

Tap "Setting" button, it is displayed the function description and the measurement settings in Info view. To return to the previous screen by tapping "Close" button.


Release Note

Version 6.0.1 was released on October 2, 2023 UTC.
Version 6.0 was released on September 28, 2023 UTC.
Version 5.1 was released on October 21, 2022 UTC.
Version 5.0 was released on September 28, 2022 UTC.
Version 4.1 was released on October 28, 2021 UTC.
Version 4.0 was released on October 20, 2021 UTC.
Version 3.3 was released on February 10, 2021 UTC.
Version 3.2 was released on November 2, 2020 UTC.
Version 3.1 was released on May 16, 2020 UTC.
Version 3.0 was released on May 14, 2020 UTC.
Version 2.1 was released on March 30, 2019 UTC.
Version 2.0 was released on November 13, 2018 UTC.
Version 1.2 was released on May 18, 2018 UTC.
Version 1.1 was released on March 14, 2018 UTC.
Version 1.0 was released on December 12, 2017 UTC.


This app is adjusted the reference value for iPhone. However, the built-in microphone of your iPhone is likely to have a non-uniform gain. The more exact measurement should be calibrated using the absolute level calibration devices.
The standard noise measurement range is 30-130dBA, and the measured value (Leq) is about 30dBA in a quiet room of the household. Due to the presence of background noise, noise levels are never measured at 0dBA even in very quiet environments..

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