Support / LFD App

Low Frequency Detector


"Low Frequency Detector" is a new acoustic measurement tool for detecting low frequency sound/noise that is hard to hear in the normal situation. It supports very lower frequency range less than 100Hz by our proprietary sound sensing technology. This app can also display the frequency component of the low frequency sound by examining by 1/3 octave band analysis and FFT analysis.

The human ear is insensitive enough to become a low frequency. If you may be exposed to the noise of neighboring constructions and factories without noticing, you may have a feeling bad and a sense of oppression. In this case, you can check what type of low frequency noise exists by simple operation of this app.

In the latest version, the analysis report function is now available.

lfd_time lfd_oct lfd_fft

Please to click the following link to download "Low Frequency Detector" from App StoreTM. It will be open the download page on App StoreTM.

It will move to another site, download from Apple Store

Communications charges when connecting to the App Store will be borne by the customer.
iPhone, AirPlay is a trademark of Apple Inc., registered in the U.S. and other countries. App Store is a service mark of Apple Inc.

Products Information

Version : 2.0
Release date : December 12, 2018. UTC
Size : 0.5 MB
Category : Utilities, Life Style
Recommendation : Compatible with iPhone. Requires iOS 12.1 or later. iPod and iPad products are not recommended.


Optimized for iPhone, Compact code size.
Low frequency power level measurement from 5Hz to 100Hz (LF Level): Flat characteristic, Updating indication of measurement period 1sec.
Power level measurement in the audible band (Leq): Flat characteristic, Updating indication of measurement period 200ms.
1/3 octave band analysis (Oct)
FFT analysis (FFT)
Time course graph (TIME)
Snapshot (Snap) on the measurement display screen.
Report function (Report): Analysis report of a peak LF Level with TIME, OCT and FFT.
Measurement time : up to 60 sec.

Low Frequency Sound

In general, the low frequency sound is a sound wave with 1 Hz to 100 Hz. By depending on its frequency component and sound level, it is different the degree of influence on the human body and the noise sensation. This app can also display the frequency component of the low frequency sound by examining by 1/3 octave band analysis and FFT analysis.

Operation procedure

Measurement analysis of low frequency sound is performed in the following step. Be sure to set the measurement conditions in Step 1) and Step 2) once before starting the measurement analysis.

1) Tuning (Reference signal adjustment)

Adjust the hardware volume of the iPhone and adjust the playback sound of the reference tone 1 kHz to fit the power level bar between 40 to 60.


2) Calibration

Signal calibration is performed in as quiet a sound environment as possible. It takes 15 seconds and stops automatically. The measured value at this time is applied as the reference noise level, so this app measures the relative noise value for the low frequency range. The previous calibration information can be maintained.

The accuracy of the measument condition is displayed after the calibration is complete.

"Completed !" : Normal
"Terminated.(low accuracy)" : Low accuracy


3) Measure

In low frequency sound measurement, it analyzes the ambient sound from the built-in microphone while playing the reference signal (1kHz). Perform measurements in places where low frequency noise is expected to occur. This measurement is automatically stopped within the time specified in the timer setting.

4) Measurement display

The measurement indication can select either 1/3 octave band frequency analysis, FFT analysis, or low frequency sound level time transition chart. These measurement analysis displays are updated in real time. In addition, after the completion of the measurement, you can show the analysis report.


Sound Level

The sound level shows the power level (Leq) of the audible band and the low frequency power level (LF Level) less than 100 Hz. At this time, these update period are "Leq" with 0.2 seconds and "LF Level" with 1 second.

LF Level (dB): Low frequency power level less than 100Hz.
Leq (dB): Sound power level with the frequency weight characteristic Z (Flat) of the audible band.


1/3 Octave Band Analysis (OCT)

In this analysis, the power spectrum in the low frequency sound is displayed by the frequency component band that is divided into fourteen from the center frequency 5Hz to 100Hz. This display is updated in real time, and you can intuitively grasp the frequency component of low frequency sound. In addition, the white line display shows the frequency characteristic with the frequency weight corrected for the G characteristic.


FFT Analysis (FFT)

In this analysis, FFT analysis (Fast Fourier Transform) is performed on the low frequency sound, and the power for each frequency component is displayed in spectrum so that the instantaneous frequency peak can be observed. This display is updated in real time, and you can intuitively grasp the frequency component of low frequency sound. In addition, the white line display shows the frequency characteristic with the frequency weight corrected for the G characteristic.


Time course graph (TIME)

In this analysis, the time transition of the observed low frequency sound power level (LF Level) is displayed as a graph chart. The vertical axis shows the power level and the horizontal axis updates and displays in real time.


Analysis Report (Report)

After the completion of the measurement, you can display the report of peak LF Level analysis. It is effective when measuring for 10 seconds or more.

Time course graph : TIME

- Low frequency (LF) Level (dB): Time course graph. It also shows the noise level judgment (RED-very noisy, YELLOW-noisy, GREEN-normal) at the peak level.

- LF max (dB) : maximum dB value of low frequency.

Frequency response graph : OCT, FFT

- OCT Band LF max (dB): maximum dB value in 1/3 octave band at LF max observation.

- Max Level Frequency (Hz): peak frequency at LF max observation.


Snap Shot

By tapping Snap button, you can save the current measurement display to "Photos". Time information is also imported into the image.

Product Information

By tapping "Info" button, it is displayed the product information. If you tap the "Support", Safari starts and you can see our support page.

Release Information

Version 2.0 was released on December 12, 2018. UTC
Version 1.4 was released on May 18, 2018. UTC
Version 1.3 was released on April 17, 2018. UTC
Version 1.2 was released on February 25, 2018. UTC
Version 1.1 was released on May 9, 2017. UTC
Version 1.0 was released on January 26, 2017. UTC


Sound measurement of the low frequency range is a level difference with respect to the reference signal 1kHz, which indicates the relative power value. The frequency characteristic of the low frequency measurement is the flat characteristic.
The white line in the OCT and FFT modes indicates frequency characteristics in frequency weight correction of G characteristics.
Since iPhone's built-in microphone has a lower sensitivity on the low frequency range, it is not recommended to measure a huge volume sound near a loud noise source.
Since it takes a while for the observation value to stabilize immediately after the start of measurement, the maximum value is calculated from about 2 seconds later.
In the case high power of 1kHz component is included in the measured noise source, the precision of measured value by this app largely decreases.
Sudden noise or impulsive sounds are not low frequency noises.
There are variations in analysis results due to individual differences of iPhone devices.
The authorization for access to the built-in microphone and Photos will be confirmed by the iOS system at first access. Please enable access to Microphone and Photos.

Request for review

Please send a review of your comments and requests for this app. We will use your review to improve our products. Thank you for your cooperation.

It will move to another site, download from Aplle Store Please send a review message for "Low Frequency Detector".

Please fill in your review by accessing from iOS device.

Contact us

Inquire about this app please from below!

Support contact :

Please contact us with the following details if you have any requests or problems.

1. Application name
2. Device model
3. iOS version
4. Country you live
5. Details about your requests or problems.

(note: Please enter the at sign of the mail address in lowercase letters.)

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