| Summary: | 博士 === 國立交通大學 === 電機與控制工程系 === 89 === In this thesis,
the error shaping technique and the information of spectral dynamics
between two successive frames of speech spectra are
simultaneously incorporated into
the LSF vector quantization (VQ) to
improve the performance of LSF quantizers.
The error shaping technique can be used to make better use of
the perceptual property of human ear, and
the spectral dynamics information incorporated into the LSF VQ can smooth
the spectral quantization error so as to reduce the perceived
distortion.
The error shaping technique based on
the weighted log-spectral distortion
(WLSD) measure can be used to shape the spectral
distortion distribution of quantization error
into any frequency-dependent curve depending on
what kind of weighting function is used.
The WLSD measure is approximated to a
quadratic distortion measure or the weighted mean squared error
(WMSE) measure since the high computational complexity of the WLSD measure
deters this error shaping technique from practical use.
The optimal WMSE weights (i.e., the optimal weights of LSF parameters) also are
determined based on the theoretical analysis of the WLSD measure
in this error shaping technique.
To incorporate the
information of the spectral dynamics of LPC spectra into LSF VQ,
an innovative technique is proposed.
It is based on a modified weighted log-spectral distortion (MWLSD) measure.
The MWLSD measure can be used to
shape the spectral quantization
distortion distribution
into any frequency-dependent shaping curve,
and simultaneously
reduce the spectral-dynamics distortion between quantized spectra
and unquantized spectra.
That is, both the spectral distortion and spectral-dynamics distortion
between quantized spectra and unquantized spectra
can be taken into account simultaneously in designing a quantizer
for a desired error shaping function by %using the proposed technique.
using the MWLSD measure.
In order to reduce the high
computational complexity of the MWLSD measure during the search
procedure in the LSF VQ,
a quadratically weighted distortion (QWD) measure used to
approximate the MWLSD measure is
derived based on the theoretical analysis of the MWLSD measure.
A simplified quadratically weighted distortion (SQWD) measure is also
proposed to further reduce the computational complexity of the QWD
measure for practical applications,
whose computational complexity is almost equal
to that of weighted mean square error (WMSE) measure.
The error shaping technique and the spectral dynamics information are finally applied
to the LSF quantization of CELP and MELP coders to test how it
affects the overall speech quality in actual speech coding
algorithms.
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