The following plots demonstrate overlap of recognition features in the cepstral space. These plots consist of the vowels "aa" (as in "lock") and "iy" (as in "beat") excised from tokens in the SWITCHBOARD conversational speech corpus.

In these plots, the first two cepstral coefficients are shown (c[1] and c[2]; energy, which is c[0], is not shown). Comparisons are provided as a function of the vowel spoken and the gender of the speaker:

• Vowel Comparison: a comparison of male "aa" to male "iy"
  
  
• Vowel Comparison: a comparison of female "aa" to female "iy"
  
  
• Vowel Comparison: a combined plot of the above conditions
  
  
• Gender Comparisons: a comparison of males and females for the vowels "aa" and "iy"
  
  
• Combined Comparisons: a comparison of "aa" to "iy" for both genders

The Switchboard vowel data used to generate these plots is available for classification experiments.