How Does The Doppler Effect Cause A Sirens Pitch To Increase As It Approaches You Apex?

How Does The Doppler Effect Cause A Sirens Pitch To Increase As It Approaches You Apex? As the car approaches listener A, the sound waves get closer together, increasing their frequency. This listener hears the pitch of the siren get higher. As the car speeds away from listener B, the sound waves get farther apart,