In this paper, we present results of non-uniform vowel normalization and show that the frequency-warping necessary to do nonuniform vowel normalization is similar to the mel-scale. We compare our methods to Fant’s non-uniform vowel normalization method and show that with proposed frequency warping approach we can achieve similar performance without any knowledge of the spoken vowel and the formant number. The proposed approach is motivated by a desire to perform non-uniform speaker normalization in automatic speech recognition systems. We also present results of a more comprehensive study of our earlier work on non-uniform scaling which again shows that mel-scale is the appropriate warping function. All the results in this paper are based on data from Peterson & Barney and Hillenbrand et al. vowel databases.