Figure 4: Example of a perineal sound recording in a male volunteer (reproduced from Neurourol. Urodyn., with kind permission of John Wiley and Sons, Inc.). In the example, the flow rate (a), perineal sound (b), and the frequency spectrum of the perineal noise (c) are plotted as a function of time. For each frequency (on the vertical axis) in the sound frequency spectrum red represents a high power and blue represents a low power. In the bottom, three panels the weighted average frequency (d), the standard deviation (e) and the skewness (f), derived from the sound frequency spectrum, are presented as a function of time.