Patent ID: 7792680

Claim:
A method for extending the spectral bandwidth of an excitation signal of a speech signal, comprising: determining a bandwidth limited excitation signal of the speech signal; and generating a bandwidth extended excitation signal based on the bandwidth limited excitation signal by applying a quadratic function to the bandwidth limited excitation signal where the quadratic function is: {tilde over (x)} Anr,i ( n )= c 2 ( n ) x 2 p,i ( n )+ c 1 ( n ) x p,i ( n ), where c 1 and c 2 are determined according to the following relations: c 1 ⁡ ( n ) = K 1 - x max ⁡ ( n ) ⁢ c 2 ⁡ ( n ) = K 1 - x max ⁡ ( K 1 - K 2 x max ⁡ ( n ) - x min ⁡ ( n ) + ɛ ) , ⁢ and c 2 ⁡ ( n ) = K 1 - K 2 x max ⁡ ( n ) - x min ⁡ ( n ) + ɛ , where x max =Maximum value of input signal vector x p , x min =Minimum value of input signal vector x p , ε>0, n=time, K 1 =Constant for determining maximum value after applying quadratic function to speech signal, K 2 =Constant for determining minimum value after applying quadratic function to speech signal, i =segment of signal, and x p,i (n)=Portion of i of spectrally flat excitation signal at time n.