Spectro-temporal analysis of speech signals using zero-time windowing and group delay function

• New method for estimation of vocal tract system characteristics from short segments of speech.
• Zero-time windowing using an impulse-like window function provides temporal resolution.
• Additive property of the group delay function provides the spectral resolution.
• Robust to additive noise degradations.
• Outperforms short-time Fourier analysis, LP analysis and STRAIGHT analysis methods in estimating second and third formants.

Traditional methods for estimating the vocal tract system characteristics typically compute the spectrum using a window size of 20–30 ms. The resulting spectrum is the average characteristics of the vocal tract system within the window segment. Also, the effect of pitch harmonics need to be countered in the process of spectrum estimation. In this paper, we propose a new approach for estimating the spectrum using a highly decaying window function. The impulse-like window function used is an approximation to integration operation in the frequency domain, and the operation is referred to as zero-time windowing analogous to the zero-frequency filtering operation in frequency domain. The apparent loss in spectral resolution due to the use of a highly decaying window function is restored by successive differencing in the frequency domain. The spectral resolution is further improved by the use of group delay function which has an additive property on the individual resonances as against the multiplicative nature of the magnitude spectrum. The effectiveness of the proposed approach in estimating the spectrum is evaluated in terms of its robustness to additive noise, and in formant estimation.