You can see it as a frequency analysis of the sound. If your output array is a series of complex numbers, you should compute the array of the squared modulus of the numbers and plot this array. You should obtain a graph where the x axis is the frequency of the sound and the y axix is the energy. So peaks in this graph represent the frequencies which carry the more energy in the incoming signal. The next step si to compute the scale of the frequency axis. It depends on the duration of your sample data. If you can post a plotted result of both the sample and it's fft, it would be great.