Answer:
Pitch changes are heard when the Doppler effect occurs.
Explanation:
we have to tell what changes are heard when the Doppler effect occurs.
The Doppler effect is the change in wavelength or frequency of wave in relation to an observer who is moving relative to the wave source.
An increase or decrease in the frequency of sound, light, or the other waves as source and the observer move towards or away from each other. This effect causes the sudden change in pitch.
The very common example for Doppler effect for sound is
You hear the high pitch of the siren of approaching ambulance and notice that its pitch drops suddenly as the ambulance passes you. That is called the Doppler effect.
Hence, Pitch changes are heard when the Doppler effect occurs.