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Doppler Pitch Shift is a Function of Distance, Independent of Motion.


Tracy Love:
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.

Tracy Love:
There are two aspects of sound that change as a function of distance, 1) volume (which is loudness) and, 2) perceived pitch, (which is the brain's summation of many sound frequencies). Your spectrum analyzer will verify that higher frequencies of sound attenuate (roll-off) more rapidly with distance than do lower sound wave frequencies and it is the varying summations of frequencies at varying distances that create the pitch shift known at the Doppler Shift. In the case of  a moving sound source, the source is constantly changing distance creating the familiar sound of changing pitch. By analyzing the frequency distribution at each distance, it can be seen that the Doppler Pitch Shift is a function of distance and independent of motion, which is contrary to accepted Doppler Theory.

Although the story will come out in various ways. I would like to learn even more.


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