Signal-based indicators for predicting the effect of audible tones in the aircraft sound at takeoff

Audible tones in the sound of aircraft at takeoff, perceived at ground level, generally take the form of two components. The first one is a whistling sound at a frequency that corresponds to the fan rotation multiplied by the number of blades (blade passing frequency). The second one is a series of harmonic partials with a low fundamental frequency (buzz-saw noise). In the scope of the PARASOFT project, a former study showed that these two sound components, when heard at the same loudness, can have an effect on unpleasantness. Here, the results of this study were compared with different tonality indicators (EPNL tone correction factor, ISO1996-2 annex C, DIN45681, Aures' model), and an indicator of roughness. This comparison revealed that all four tonality indicators are well suited for quantifying the detrimental impact of isolated tones. However only Aures' model for tonality, because it is not limited to the highest emergence, and roughness are able to account for the effect of buzz-saw noise. Aures' model for tonality should thus be considered when trying to predict the negative impact of any kind of audible tones in aircraft sound at takeoff.