EAN: 9783031003936

SYNTHESIS LECTURES ON ALGORITHMS AND SOFTWARE I...

Bandwidth extension of speech is used in the International Telecommunication Union G.729.1
standard in which the narrowband bitstream is combined with quantized high-band parameters.
Although this system produces high-quality wideband speech  the additional bits used to
represent the high band can be further reduced. In addition to the algorithm used in the
G.729.1 standard  bandwidth extension methods based on spectrum prediction have also been
proposed. Although these algorithms do not require additional bits  they perform poorly when
the correlation between the low and the high band is weak. In this book  two wideband speech
coding algorithms that rely on bandwidth extension are developed. The algorithms operate as
wrappers around existing narrowband compression schemes. More specifically  in these algorithms
the low band is encoded using an existing toll-quality narrowband system  whereas the high band
is generated using the proposed extension techniques. The first method relies only on
transmitted high-band information to generate the wideband speech. The second algorithm uses a
constrained minimum mean square error estimator that combines transmitted high-band envelope
information with a predictive scheme driven by narrowband features. Both algorithms make use of
novel perceptual models based on loudness that determine optimum quantization strategies for
wideband recovery and synthesis. Objective and subjective evaluations reveal that the proposed
system performs at a lower average bit rate while improving speech quality when compared to
other similar algorithms.

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