Influence of temporal aspects of aircraft sound signature on perceived unpleasantness

This paper focuses on the temporal aspects of aircraft flyover noise signals and their psychological effects. Stimuli are equalized according to EPNL: this avoids possible loudness masking effects. Features describing the temporal evolution of the sound level are studied: rising slope, duration and amount of fluctuations due to turbulences. A synthesisby-recording method supplies realistic signals, which are further processed in order to design a set of stimuli uncoupling temporal features one from another. This gives e.g. short signals with smooth slope, or long signals with sharp slope. The stimuli are rated by subjects on semantic scales handling the following sound aspects: "long / short", "sudden / gradual", "slow / fast", "steady / staccato-like", and "not unpleasant at all / extremely unpleasant". The output of the psychoacoustic test is statistically analyzed. At constant EPNL, the stimuli are perceptually organized along two dimensions. First the "duration" aspect is correlated with the length of the signal part having a sound level above PNL max-10PNdB, and with the PNL max. Second the "staccato-like" aspect (corresponding to the amount of fluctuations) is correlated with the "fluctuation strength". Moreover, it is shown that this "staccato-like" aspect contributes to the overall unpleasantness of the aircraft flyover noise.