According to a study by scientists at the University of Washington, the newborn does not hear as adults. The newborn is able to differentiate noises, but has tonal separation problems. Listen to all sound frequencies at once and often find it difficult to distinguish one sound from all others.
Adults, on the other hand, listen to the sounds and distinguish them by their origin, and draw attention to what we really want to hear. In addition, we listen in a narrower frequency band than newborns. Neonatal hearing is functional, improving hearing sensitivity up to about 10 years.