Answer: Doppler shift
Step-by-step explanation:
Doppler effect an be defined as the change in the sound waves frequency, pitch or wavelength due to the movement that is relative to the wave sound. It can be observed when a sound is approaching or receding an observer.
When any sound is far from the ear then its sound is low and when it reaches the ear its volume increases as the pitch increases.
The change in the frequency of the sound is due to Doppler's Effect.