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Picture of the Month (June 2008)
Dedicated User Captions:
1. Die schreckliche Wahrheit über die Jazzpolizei
2. You say goodbye, I say hello
3. Musik in Zeiten preussischer Bürokratie

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Influence of motion on the pitch of sounds

This picture illustrates the influence of movement on the perception of tone pitch. The author, Rodolphe Radau, explains the shift in pitch using the example of a train passing. The whistle of the engine-driver on an arriving train appears to be higher than on a departing one.

Taken 31 miles per hour as the speed of a train, this equals 1/24 of the velocity of sound. Hence, a calculation based upon this shows that an observer placed on the railroad will perceive the note of the whistle changed in the ratio of 24 : 25. The observer will either estimate it too high or too low by a semitone. What is a "la" for the engine-driver is a "la" sharp or a "la" flat for an observer, depending on the train's moving direction.

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Picture Source:
Radau, R. 1867. L'acoustique ou les phénomenes du son. Paris: L. Hachette (Staatliches Institut für Musikforschung)

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