Statistical Study of the Instantaneous Values of Traffic Noise Sound Pressure Level

In environmental acoustics the knowledge of the time dependency of the sound level provides relevant information about a sound event. In this sense, it may be said that conventional sound level metres have frequently implemented programs to calculate the fractiles (percentiles) of the distribution of instantaneous sound levels; and there are several indexes to evaluate the noise pollution, based on different statistical parameters. For further analysis of sound, and to obtain the commented indexes, it is accepted that this distribution is normal or gaussian. The questions we've tried to solve in this work are the following: First of all, whether the time dependent distribution of the variable sound pressure level should be considered as Gaussian in general cases or only in some particular ones. On the other hand, we have studied how the frequency of the sampling affects the resulting distribution of a given a sound event. To these ends, a set of road traffic noise events has been evaluated. Furthermore, even in gaussian distributions of sound pressure levels, the average of the distribution will not be coincident with the equivalent sound pressure level; that is the level of the average quadratic pressure. The difference between this parameter, and its dependence on the standard deviation, is studied.