The impact of the pitch on the estimation of MFCC

In this paper, the impact of the pitch on the variability of MFCC, and their influence on the performance of the automatic speech recognition system, is analyzed. In case that a speaker has a high pitch, the distance between adjacent harmonics in the spectrum of voiced phonemes is larger, which results in poorer description of the spectral envelope. Additional problem arises in the case that a band-pass filter from the analysis filter bank covers the range between two harmonics, capturing the part of spectrum without energy, which consequently leads to the detection of sudden, non-existing changes in the spectral envelope. The reduction of these variations is analyzed by using a lower number of MFCC, by expending the bandwidths of the band-pass filters from the filter bank at lower frequencies, and also by low-pass filtering of the filter bank output. Some of the results are somewhat different from the similar results presented in the literature, for which the adequate explanations are offered.