The pitch of a sound is decreased, when a sound source approaches the observer.
Explanation:
Pitch is nothing but it is a property that helps to determine whether the sound is high or low. Doppler effect helps to understand this concept easily. The pitch of the sound is mainly calculated based on the frequency of the sound wave arose from the sound source.
As the wellspring of sound waves moves toward an audience, the sound waves draw nearer together, expanding their recurrence and the pitch of the sound.