Narayanan, N K; Dr.Sridhar, C S(Cochin University of Science and Technology, February 17, 1990)
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Abstract:
This thesis investigates the potential use of
zerocrossing information for speech sample estimation.
It provides 21 new method tn) estimate speech samples using
composite zerocrossings. A simple linear interpolation
technique is developed for this purpose. By using this
method the A/D converter can be avoided in a speech coder.
The newly proposed zerocrossing sampling theory is supported
with results of computer simulations using real speech
data. The thesis also presents two methods for voiced/
unvoiced classification. One of these methods is based
on a distance measure which is a function of short time
zerocrossing rate and short time energy of the signal.
The other one is based on the attractor dimension and entropy
of the signal. Among these two methods the first one is
simple and reguires only very few computations compared
to the other. This method is used imtea later chapter to
design an enhanced Adaptive Transform Coder.
The later part of the thesis addresses a few
problems in Adaptive Transform Coding and presents an
improved ATC. Transform coefficient with maximum amplitude
is considered as ‘side information’. This. enables more
accurate tfiiz assignment enui step—size computation. A new
bit reassignment scheme is also introduced in this work.
Finally, sum ATC which applies switching between luiscrete
Cosine Transform and Discrete Walsh-Hadamard Transform
for voiced and unvoiced speech segments respectively is
presented. Simulation results are provided to show the
improved performance of the coder
Description:
Department of Electronics, Cochin University
of Science and Technology