Two pieces of physics that haven't heretofore been mentioned: 1) Propeller noise is fairly directional. For more on this, see http://www.google.com/search?q=propeller+noise+directivity
This means that when a Real World aircraft flies past, you will hear a more rapid build-up and more rapid fall-off than could be explained by the basic 1/r^2 dependence. Note that the same physics sometimes produces no effect or even the opposite effect for helicopters, depending on whether the geometry is fly-by or fly-over. On the other hand, keep in mind that the propeller is not the only source of noise. There is also a lot of engine noise. Piston engine noise is not usually so directional. FWIW note that recent versions of the FG c182rg have separate models for engine noise and propeller noise, as you can easily observe by running at high RPM and then pulling the mixture. 2) In polar coordinates, the wave equation is _dispersive_, even though in rectangular coordinates it is non-dispersive. Spherical Bessel functions are different from plane waves. The dispersion changes the timbre of the sound. This is why people far away from an explosion think high explosives go "boom" even though up close they don't go "boom" at all; they go "SNAP!" If you were serious about modeling flyby sounds, you would need to account for this. In principle it might not even be hard; you could probably do a lot with an all-pass phase shifter with a movable tap. In practice, it's a mess. Digital filters benefit a lot from MMX instructions ... but then you run into portability problems. asoundlib has pitch bender functions built in (for Doppler) but last time I checked it didn't support arbitrary digital filters. ------------------------------------------------------------------------------ This SF.net email is sponsored by: SourcForge Community SourceForge wants to tell your story. http://p.sf.net/sfu/sf-spreadtheword _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
