the Doppler effect
the Doppler effect is what happens when an object that is moving is producing sound. has a police car, ambulance or firetruck ever passed by you when their sirens are blaring? When their car passes you, the sound waves that the car is producing are getting bunched up in the front of it because that car is moving towards those waves. creating a high pitch of sound. behind the car, the sound waves are getting spaced out and creating a lower pitch. this is a visual representation under here
sound interference
Sound interference is when two sound waves playing the same frequency interact with each other and either bring the amplitude up or lower it to nothing. the difference is timing and placement. if the sound waves are not the same and the top of one hits the bottom of another sound wave, destructive interference comes into play. If the sound waves line up with each other, constructive interference happens. constructive interference is what brings the amplitude up and destructive interference makes no sound and destroys the wave.
the image above is a visual representation of the sound interference.