5. The method of claim 1 , further comprising determining a targeted set of spectral features based on phonetic properties that distinguish the target problematic phoneme from other phonemes.
5. The method of claim 1 , further comprising determining a targeted set of spectral features based on phonetic properties that distinguish the target problematic phoneme from other phonemes. 7. The method of claim 5 , wherein the targeted set of spectral features includes one or more of spectra values, cepstra values, mel-scaled cepstra coefficients, power normalized cepstral coefficients, a pitch value, a signal-to-noise ratio (SNR), a voice strength estimate, and a voice period variance estimate.