"Low Frequency Detector" is a new acoustic measurement tool for detecting the low frequency sound that is hard to hear in the normal situation.
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 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.
"Low Frequency Detector" can also display the frequency component of the low frequency sound by 1/3 octave band analysis and FFT analysis.
In the latest version, the analysis report function is now available.
- Low frequency power level measurement less than 100Hz (LF Level): Flat characteristic, Updating indication of measurement period 1 sec.
- 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.
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 sound measurement analysis.
1) Tuning: Reference signal adjustment. Set the hardware volume so that "Leq" graph bar fits from 40 to 60.
2) Calibration: Determining the reference of the noise level of low frequency band.
3) Measure: Analyze low frequency sound level.
- 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.
4) Measurement display: Measurement indication can select either 1/3 octave band frequency analysis, FFT analysis, or Time course graph. These displays are updated in real time.
5) 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.
- 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.
- 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 very low frequency range, it is not recommended to measure a huge volume sound near a very 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.
- The previous calibration information can be maintained.
- There are variations in analysis results due to individual differences of iPhone devices.
- The authorization to access built-in microphone and Photos will be confirmed by iOS system at first boot.
- Changed UI.
- Some improvements.
- Requires iOS12.1 or later.