This study's aim was to determine if 6- and 9-month-old infants discriminate approximants and vowels when the spectral shape is modified to emphasize high- or low-frequency information. Infants were presented with /r/-/l/ and /ɔ/-/ɐ/ in three conditions: (a) unmodified; (b) -6 dB/octave tilt; and (c) +6 dB/octave tilt. Six-month-olds discriminated /ɔ/-/ɐ/ in conditions (a) and (b), and /r/-/l/ in conditions (a) and (c), but 9-month-olds only discriminated when unmodified. The results reflect native-language attunement. Six-month-olds discriminate spectrally modified sounds that emphasize relevant cues, but by 9 months, infants are sensitive to the native spectral profiles of speech.