according to the doppler effect the sound of a police car siren is
Doppler effect The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer John Dobson explained the effect thus:
Ä Ä (lower case ä) is a character that represents either a letter from several extended Latin alphabets, or the letter A with an umlaut mark or diaeresis.
My Ántonia
Marcus Álvarez