On the perception of crackle in noise radiated from military jet aircraft

Abstract

Crackle, a phenomenon sometimes associated with supersonic jet noise, has been usually quantified using the time waveform skewness. Skewness is a measure of the asymmetry of the waveform probability density function (PDF). This paper discusses whether skewness is a sufficient descriptor for the perception of crackle in jet noise waveforms. As part of this study, methods by which non‐Gaussian waveforms may be generated have been investigated. By passing a Gaussian noise signal through an appropriately selected nonlinear transformation function, a simulated waveform can be created that has the same mean, variance, skewness, kurtosis, and power spectrum as a crackle‐containing F/A‐18E waveform recorded 18 m from the aircraft during a tie‐down test. In addition, the PDFs of the simulated signal and the recorded signal are nearly identical. Despite the essential equivalence of the two waveforms from a statistical and spectral perspective, there is no perceived crackle when the simulated waveform is played back. Further analysis of the two waveforms suggests that perception of crackle is likely related to rapid changes in acoustic pressure that reveal themselves in the characteristics of the time derivative of the waveform than of the waveform itself. [Work supported in part by SERDP and ONR.]