Hi Oy, the way that I've done this is to take teh sound file and make several copies of it from GoldWave and increase the amplitude a little each time I copyit into seperate files like Sound1.wav,Sound1.wav,Sound2.wav,Sound3.wav,Sound4.wav,Sound5.wav and call them in sequence as the object get closer: you can get goldwave at: www.goldwave.com

 This tool lets you make great, edit, modify sounds for any kind for program you mite wont to make.

Thanks again Oy great questions.