FFT is a high-resolution audio analysis tool available as an in-app purchase in AudioTools. It uses the Fast Fourier Transform (see below) to analyze incoming audio, and displays a very detailed graph of amplitude vs. frequency. This application has been designed for acoustics work, and so the FFT bins have been normalized to octaves, to get a display that will show a flat line for pink noise. You can control both the level of graph smoothing and decay time, to get as much or as little detail as you require.