Some considerations and information are provided on the previously proposed algorithm for computing the physical descriptor (Lφ) of environmental impulsive sounds. This parameter can be directly measured by a microprocessor-based apparatus recently presented in this Journal [G. B. Cannelli and S. Santoboni, J. Acoust. Soc. Am. 90, 1464–1468 (1991)], but its analytical formulation, as it is given in the above-mentioned paper, needs further improvements in order to fit in perfectly with the working of the instrument. The definitive formulation of Lφ is given here together with an example which clarifies the concept of ‘‘noise fluctuation level’’ and illustrates the way of computing this physical descriptor. Some preliminary laboratory tests are also reported.