Sub-band cepstral distance as an alternative to formants: Quantitative evidence from a forensic comparison experiment

This paper demonstrates the potential of the sub-band parametric cepstral distance (PCD) formulated by Clermont and Mokhtari (1994), as an alternative to formants in acoustic phonetic research. As a cepstrum-based measure, the PCD is automatically and reliably extracted from the speech signal. By contrast, formants are time-consuming and often difficult to estimate, a well-known bottleneck for studies based on large-scale datasets. The PCD measure gives flexibility in selecting the frequency limits of any sub-band of interest within the available full band. We suggest that, if sub-band selection were guided by the acoustic–phonetic theory of speech production, PCD analysis could facilitate phonetically meaningful cepstral comparisons without relying directly on formants. We evaluate this idea by exploiting the PCD properties in the context of forensic voice comparison as an application example. The cepstral data were obtained from the vowels uttered by 306 male Japanese speakers. Similar patterns of results were observed using formants and sub-band PCDs, the latter yielding better performance. This suggests that sub-band PCDs are able to capture the spectral characteristics that we normally quantify through formants, but with better reliability and efficiency. The PCD results reported here are encouraging for other types of acoustic phonetic studies in which comparisons of spectral characteristics are required.