I made this software for the company (Lozej d.o.o.) that's doing measurements and studies of noise influence area. I wrote it in Delphi. For calculation it needs ground plan in jpeg format, from which you have to know at least one real dimension for scale calculation. With mouse you place noise sources and then define them the level in dB. After all this placed the program can calculate and draw the boundary of where to certain height of noise extends. Simple said program calculates on which distance form the source noise level drop to certain level.
Unfortunately i lost the source code, so i not developing it any more.