The sensitive period for phonetic learning, evidenced by improved native speech processing and declined non-native speech processing, represents an early milestone in language acquisition. We examined the extent that sensory encoding of speech is altered by experience during this period by testing two hypotheses: early sensory encoding of non-native speech declines as infants gain native-language experience, and music intervention reverses this decline. We longitudinally measured the frequency-following response, a robust indicator of early sensory encoding along the auditory pathway, to a (...) Mandarin lexical tone in 7- and 11-months-old monolingual English-learning infants. Infants received either no intervention or music intervention randomly between FFR recordings. The language-experience group exhibited the expected decline in FFR pitch-tracking accuracy to the Mandarin tone, while the music-intervention group did not. Our results support both hypotheses and demonstrate that both language and music experiences alter infants’ speech encoding. (shrink)