A system and method are disclosed for extending the bandwidth of a narrowband
signal
such as a speech signal. The method applies a parametric approach to bandwidth
extension but does not require training. The parametric representation relates
to a discrete acoustic tube model (DATM). The method comprises computing narrowband
linear predictive coefficients (LPCs) from a received narrowband speech signal,
computing narrowband partial correlation coefficients (parcors) using recursion,
computing Mnb area coefficients from the partial correlation coefficient,
and extracting Mwb area coefficients using interpolation. Wideband parcors
are computed from the Mwb area coefficients and wideband LPCs are computed
from the wideband parcors. The method further comprises synthesizing a wideband
signal using the wideband LPCs and a wideband excitation signal, highpass filtering
the synthesized wideband signal to produce a highband signal, and combining the
highband signal with the original narrowband signal to generate a wideband signal.
In a preferred variation of the invention, the Mnb area coefficients
are converted to log-area coefficients for the purpose of extracting, through shifted-interpolation,
Mwb log-area coefficients. The Mwb log-area coefficients
are then converted to Mwb area coefficients before generating the wideband parcors.
