Even before birth, babies have been shown to respond to sound stimuli within a limited range of sound frequencies. At birth, most babies hear quite well with the exception of very quiet sounds.
Aslin, R. N., Pisoni, D. B., & Jusczyk, P. W. (1983). Auditory development and speech perception in infancy. In Haith. M. M., & Campos, J. J. (Eds.), Handbook of child psychology, 2. Infancy and developmental psychobiology. New York: Wiley.
Peck, J. E. (1995). Development of hearing. Part III. Postnatal development. Journal of the American Academy of Audiology, 6, 113