Which of the following will cause a change in pitch when a sound is approaching or receding?
absolute magnitude
doppler shift
emission spectrum
parallax

Doppler shift

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.

gold i'm pretty sure i might be wrong