The objective of this paper is to demonstrate the importance of positi
on of the analysis time window in time-frequency analysis of speech si
gnals. Speech signals contain information about the time varying chara
cteristics of the excitation source and the vocal tract system. Resolu
tion in both the temporal and spectral domains is essential for extrac
ting the source and system characteristics from Speech signals. It is
not only the resolution, as determined by the analysis window in the t
ime domain, but also the position of the window with respect to the pr
oduction characteristics that is important for accurate analysis of sp
eech signals. In this context, we propose an event-based approach for
speech signals. We define the occurrence of events at the instants cor
responding to significant excitation of the vocal tract system. Knowle
dge of these instants enable us to place the analysis window suitably
for extracting the characteristics of the excitation source and the vo
cal tract system even from short segments of data. We present a method
of extracting the instants of significant excitation from speech sign
als. We show that with the knowledge of these instants it is possible
to perform prosodic manipulation of speech and also an accurate analys
is of speech for extracting the source and system characteristics.