Decomposition of speech signals for analysis of aperiodic components of excitation

The motivation for this study is the need for careful analysis of aperiodicity of the excitation component in expressive voices. The paper proposes analysis methods which can preserve the excitation information corresponding to sequence of impulse-like excitation with variable strengths. To analyze the details of the excitation source characteristics, the epochs and the strength of the excitation at the epochs are obtained using the output of an ideal zero-frequency digital resonator. The vocal tract system characteristics are derived from the signal between two successive epochs using the numerator of the group delay function. The spectrogram of the zero-frequency filtered signal and the group delay spectrum correspond to characteristics of the excitation and the vocal tract system, respectively. Decomposition of the speech signal into these two components bring out the features of excitation and vocal tract system, which can be used to explain the perception of expressive voices in terms of features of aperiodicity, pitch, harmonics and sub-harmonics. The decomposition method is illustrated using examples from linguistically significant glottalized sounds (glottal stops and ejectives), singing voices and Noh voice.