US 5,455,888 AGranted

Speech bandwidth extension method and apparatus

AssigneeNorthern Telecom Limited

InventorsVasu Iyengar, Rafi Rabipour, Paul Mermelstein, Brian R. Shelton

Life of this patent

Estimating the term…

Loading patent…

Abstract

A speech bandwidth extension method and apparatus analyzes narrowband speech sampled at 8 kHz using LPC analysis to determine its spectral shape and inverse filtering to extract its excitation signal. The excitation signal is interpolated to a sampling rate of 16 kHz and analyzed for pitch control and power level. A white noise generated wideband signal is then filtered to provide a synthesized wideband excitation signal. The narrowband shape is determined and compared to templates in respective vector quantizer codebooks, to select respective highband shape and gain. The synthesized wideband excitation signal is then filtered to provide a highband signal which is, in turn, added to the narrowband signal, interpolated to the 16 kHz sample rate, to produce an artificial wideband signal. The apparatus may be implemented on a digital signal processor chip.

Claims15

Dependent claims

Speech bandwidth extension apparatus comprising:

an input for receiving a narrowband speech signal sampled at a first rate;
LPC analysis means for determining, for a speech frame having a predetermined duration of the speech signal, LPC parameters a.sub.i ;
inverse filter means for filtering each speech frame in dependence upon the LPC parameters for the frame to produce a narrowband excitation signal frame;
excitation extension means for producing a wideband excitation signal sampled at a second rate in dependence upon pitch and power of the narrowband excitation signal;
lowband shape means for determining a lowband shape vector in dependence upon the LPC parameters;
voiced/unvoiced means for determining voiced and unvoiced speech frames;
gain and shape vector quantizer means for selecting predetermined highband shape and gain parameters in dependence upon the lowband shape vector for voiced speech frames and selecting fixed predetermined values for unvoiced speech frames;
filter bank means responsive to the selected highband shape and gain parameters for filtering the wideband excitation signal to produce a highband speech signal;
interpolation means for producing a lowband speech signal sampled at the second rate from the narrow band speech signal;
and
adder means for combining the highband speech signal and the lowband speech signal to produce a wideband speech signal.

8 more elements

A method of speech bandwidth extension comprising the steps of:

analyzing a narrowband speech signal, sampled at a first rate, to obtain a spectral shape of the narrowband speech signal and an excitation signal of the narrowband speech signal;
extending the excitation signal to a wideband excitation signal, sampled at a second, higher rate in dependence upon an analysis of pitch of the narrowband excitation signal;
correlating the narrowband spectral shape with one of a plurality of predetermined highband shapes and one of a plurality of highband gains;
filtering the wideband excitation signal in dependence upon the predetermined highband shape and gain to produce a highband signal;
interpolating the narrowband speech signal to produce a lowband speech signal sampled at the second rate;
and
adding the highband signal and the lowband signal to produce a wideband signal sampled at the second rate.

4 more elements

Dependencies are inferred from the claim text.