VOA慢速英语:跟婴儿谈话的好处

pitch - n. the highness or lowness of a sound

emphasis - n. a forceful quality in the way something is said or written

shift- v. to change or move

unique - adj. very special or unusual

silky - adj. very smooth

gravelly - adj. having a rough sound

vocal tract - n. is used by humans to create sound