Auralisation of airplanes considering sound propagation in a turbulent atmosphere

Sammanfattning: Aircraft noise is a major issue in urban areas. Due to a rising level ofurbanisation and the continuing growth of air traffic more people are exposed toaircraft noise than ever. Methods currently used for assessing theimpact of aircraft noise on humans consider mostly energetic quantities, and not thedynamic character of the sound. Therefore, in order to obtain a more accuratepicture of the impact of aircraft sound it may be helpful to assess how the audiblesound is perceived.Auralisation is a method for rendering audible sound fields and may be used tocreate audible aircraft sound. A tool was developed to auralise the sound of jetairplanes and consists of an outdoor sound propagation model and an emission synthesiser.The emission synthesiser computes an emission signal consisting of tonalcomponents and broadband noise. The spectral components vary over time and takeinto account directivity.An inverse propagation model was developed to compute back from a receiver tosource in time-domain. An automated procedure was developed to extract featuresfrom the resulting signal. These features were then used to directly synthesisethe emission as function of time, and this signal was propagated to the originalreceiver resulting in an auralisation that should reproduce the recordingit is based on.To validate the auralisation tool, a listening test was conducted where participantswere presented with recordings and auralisations and had to rate their similarity.Results indicate that differences exist between the auralisations and recordings.Improving the synthesis of the blade passing frequency is expected to improve the similaritybetween auralisations and recordings.Finally, fluctuations can typically be noticed when listening to sound from adistant aircraft, and one cause of these fluctuations is atmospheric turbulence.A computationally fast algorithm was developed to take into account theamplitude and phase modulations that arise as the sound propagates through theturbulent atmosphere. According to the author the method results in improvedplausibility of the auralisations.