JGFFTViewer_ app for iPhone and iPad

JGFFTViewer is a live FFT viewer to see the frequencies in sound around you and a noise meter(or sound meter). You can also view the actual waveform of the audio signal.

Each test of frequencies at 4kHz and 8kHz can be generated respectively by tapping its button on the top of the screen. To stop checking the waveform, tap the Stop button below the frequencys graph.

JGFFTViewer uses an algorithm of the Fast Fourier Transform to analyze frequencies.

You can perform this app with the internal microphone (iPhone). The decibel (dB SPL) in audio measurement can be inspected by you. If the curved line of frequencies becomes a colored line in red, then it tell you that the environment around you is not quiet, or not suitable to have a time you have to concentrate.