Doppler shift will cause a change in pitch when a sound is approaching or receding.
Doppler shift (also known as the Doppler effect) is the change in sound wave frequency or wavelength due to movement relative to the wave source. Doppler shift will cause a change in pitch when a sound approaches or recedes from an observer. An example is when an ambulance is moving towards a person, the frequency of the waves increases and the person hears a higher pitch but as the ambulance moves away, the frequency reduces and the person will hear a lower pitch. The change in the frequency of the sound wave because of movement is the Doppler shift.
