Low Frequency Detector

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.
This app can also display the frequency component of the low frequency sound by examining by 1/3 octave band analysis and FFT analysis.

Features:
  - Low frequency power level measurement less than 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 transition chart (Time) for displaying the relative sound level of low frequency sound
  - Timer measurement (Sec): 10 - 60 sec / 10 sec unit.
  - Instantaneous maximum value display (Max)
  - Snapshot (Snap) on the measurement display screen.

How to Use :
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 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.

3) Measure: 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 call the maximum instantaneous value in the Max button.

Notes:
- 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 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.
- The previous calibration information can be maintained.
- 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.