At this stage, your baby is growing with many new milestones. The various coordination of eyes, hand and brains are the most effective ones. With this your child has started understanding the difference between familiar and unfamiliar sounds.
What you need to know
Your baby now responds to sounds---be it familiar or unfamiliar. He will quickly respond to a familiar sound with excitement and a throaty sound. He also responds to an unfamiliar sound which is soothing. He stops playing or sucking his hands when he hears some familiar sounds. He becomes attentive and responds to sounds in his own special cooing and babblings.
He also startles to loud and sudden noises. So it is very important to be slow in our speech to him. Introduce various types of sounds so that he has knowledge of the the different sounds. Play with him. Give him toys which move, make sounds and interests him.