A simple experiment: 440 feet of straight, secluded road, 11 pylon markers, a car with horn (sound source), a video camera. Place the camcorder at the zero marker off to the side of the road. Place pylon markers at 44 feet intervals. You will need to do two recordings of the car, the first bringing the car up to 30mph before reaching the most distant pylon which is 440 feet away. 30mph is 44 feet per second so that the first recording of the sound source (blowing car horn) will yield a 10 second recording of the car moving toward the camcorder. Now for the stationary recording, take the car back to the most distant pylon 440 feet away, stop, and record for 1 second. Pull the car to the next pylon and successively make a total of ten, 1 second recordings of the car horn, one at each distance. When finished with the stationary recordings, this will give you two recordings, each ten seconds long for comparison of the sound source both in motion and stationary. This comparison shows that the perceived pitch is identical at each pylon marker distance whether the sound source (car horn) is in motion or stationary. This is a subjective, auditory comparison to first convince yourself, and then the recordings can be viewed in a spectrum analyzer for hard data comparison.