Granted Patent B2

US 7,756,714 · App. 11/701,184 · Granted Jul 13, 2010

Abstract

Claims (31)

1. A method in a telecommunication system for extending a spectral bandwidth of a bandwidth limited audio signal (x(n)) having at least one harmonic of a fundamental frequency, the method comprising:

applying using a processor a nonlinear function to the bandwidth limited audio signal to generate an extended audio signal x n1 (n), the non-linear function being a quadratic equation:

x n1 ( n )= c 2 ( n ) x 2 ( n )+ c 1 ( n ) x ( n )+ c 0 ( n ),

the coefficients c 0 , c 1 , c 2 depending on time n, wherein the application of the nonlinear function to the bandwidth limited speech signal results in a first extended speech signal,

the coefficients being determined in such a way that

c 0 ( n )=− x mit (n−1),

c 1 ( n )= K n1,1 − c 2 ( n ) x max ( n ), and

c 2 ( n )=( K n1,2 )/( g max x max ( n )+ε),

wherein K n1,1 , K n1,2 , g max and ε are predetermined constants, x max (n) is the short time maximum of the absolute value of the bandwidth limited audio signal, and x mit (n) is the short time mean value of the quadratic function.

2. The method of claim 1 further comprising the step of removing a constant component after applying the nonlinear function to the bandwidth limited audio signal.

3. The method of claim 1 further comprising the step of high-pass filtering the extended audio signal.

4. The method of claim 1 further comprising the step of low-pass filtering the extended audio signal to obtain a low frequency audio signal.

5. The method of claim 4 further comprising the step of adding the low frequency audio signal to the bandwidth limited audio signal to obtain an improved bandwidth extended audio signal.

6. The method of claim 1 further comprising the steps of: determining a lower end of the spectral bandwidth of the bandwidth limited audio signal; and if a predetermined frequency spectrum is not contained in the bandwidth limited audio signal, generating a low frequency component and adding the low frequency component to the bandwidth limited audio signal to obtain an improved bandwidth extended audio signal.

7. The method of claim 6 further comprising providing a low-pass filter for filtering out frequency components comprised in the bandwidth limited audio signal, and adjusting the low-pass filter in accordance with the lower end of the spectral bandwidth of the bandwidth limited audio signal.

8. The method of claim 6 further comprising the determining a mean fundamental frequency of the bandwidth limited audio signal; providing a high-pass filter for filtering out frequency components below a pre-determined value; and adapting the high-pass filter based on the mean fundamental frequency.

9. The method of claim 1 , where the bandwidth limited audio signal is a speech signal transmitted via a telecommunication network.

10. A system for extending the spectral bandwidth of a bandwidth limited audio signal having at least one harmonic of a fundamental frequency, the system comprising:

a determination unit for determining a maximum signal intensity of the bandwidth limited audio signal;

a processing unit for applying a nonlinear function to the bandwidth limited audio signal for generating the lower frequency components of the speech signal which are lower than a predetermined signal component, the non-linear function being a quadratic equation:

x n1 ( n )= c 2 ( n ) x 2 ( n )+ c 1 ( n ) x ( n )+ c 0 ( n ),

the coefficients c 0 , c 1 , c 2 depending on time n, wherein the application of the nonlinear function to the bandwidth limited speech signal results in a first extended speech signal,

the coefficients being determined in such a way that

c 0 ( n )=− x mit (n−1),

c 1 ( n )= K n1,1 − c 2 ( n ) x max ( n ), and

c 2 ( n )=( K n1,2 )/( g max x max ( n )+ε),

wherein K n1,1 , K n1,2 , g max and ε are predetermined constants, x max (n) is the short time maximum of the absolute value of the bandwidth limited audio signal, and x mit (n) is the short time mean value of the quadratic function.

11. The system of claim 10 further comprising a high-pass filter for obtaining a high-pass filtered signal.

12. The system of claim 11 further comprising a low-pass filter for obtaining a low-pass filtered signal; and an adder for adding the low-pass filtered signal to the bandwidth limited audio signal.

13. The system of claim 10 , further comprising a bandwidth determination unit for determining the bandwidth of the bandwidth limited audio signal.

14. The system of claim 10 , further comprising a fundamental frequency determination unit for determining the mean fundamental frequency of the bandwidth limited audio signal.

Assignments (9)