Granted Patent B2

US 8,160,889 · App. 12/015,907 · Granted Apr 17, 2012

Abstract

Claims (28)

1. A digital-controller-implemented method for providing increased bandwidth, in a digitally sampled acoustic speech signal having a restricted bandwidth, so as to improve intelligibility of the speech signal, the method comprising:

using a digital-controller-implemented spectral shifter, coupled to the speech signal to generate digitally an upper bandwidth extension signal in which at least a portion of the speech signal is shifted upwardly by a predetermined shifting frequency value, and wherein the spectral shifter is configured to perform a cosine modulation of the speech signal;

using a first digital-controller-implemented high pass filter, coupled to an output of the spectral shifter, so as to digitally generate a filtered upper bandwidth extension signal by filtering the upper bandwidth extension signal to remove frequency components below a shifter output cutoff frequency;

using a second digital-controller-implemented high pass filter, disposed between the speech signal and the spectral shifter, to remove frequency components to the spectral shifter that are below a shifter input cutoff frequency; and

generating digitally an extended bandwidth speech signal based on the speech signal and the filtered upper bandwidth extension signal.

2. The method of claim 1 , where the cutoff frequency for the first high-pass filter, used to filter the upper bandwidth extension signal, corresponds to the sum of the shifter input cutoff frequency plus and the predetermined shifting frequency value.

3. The method of claim 1 , wherein generating the extended bandwidth speech signal comprises using a digital-controller-implemented summer to generate a weighted sum of the speech signal and the filtered upper bandwidth extension signal.

4. The method of claim 3 , where weights used in the weighted sum are time dependent.

5. The method of claim 3 , where the filtered upper bandwidth extension signal is weighted with a first factor, and where the first factor is a function of an estimated signal-to-noise ratio of the speech signal.

6. The method of claim 5 , where the first factor is a monotonically increasing function of the estimated signal-to-noise ratio of the speech signal.

7. The method of claim 5 , where the filtered upper bandwidth extension signal is weighted with a second factor, and where the second factor is a function of an estimated noise level in the upper bandwidth extension signal or the filtered upper bandwidth extension signal.

8. The method of claim 7 , where the second factor is a monotonically decreasing function of the estimated noise level in the upper bandwidth extension signal or the filtered upper bandwidth extension signal.

9. The method of claim 7 , where the estimated signal-to-noise ratio or the estimated noise level are estimated based on the respective short time signal power.

10. The method of claim 7 , where the filtered upper bandwidth extension signal is weighted with a third factor, and where the third factor is based on a ratio of an estimated signal level of the speech signal to an estimated signal level of the upper bandwidth extension signal or the filtered upper bandwidth extension signal.

11. The method of claim 10 , where the third factor is a monotonically increasing function of the ratio of the estimated signal level of the speech signal to the estimated signal level of the upper bandwidth extension signal or the filtered upper bandwidth extension signal.

12. The method of claim 3 , where the speech signal is weighted by a weighted sum of the speech signal at a current time and at the current time minus one time step.

13. The method of claim 12 , where weights used in the weighted sum of the speech signal at the current time and at the current time minus one time step are functions of an estimated signal-to-noise ratio of the speech signal or of an estimated noise level in the upper bandwidth extension signal or the filtered upper bandwidth extension signal.

14. The method of claim 1 , further comprising generating a lower bandwidth extension signal for extending the speech signal at lower frequencies.

15. The method of claim 14 , where the act of generating the lower bandwidth extension signal comprises applying a nonlinear quadratic characteristic on the acoustic signal.

16. The method of claim 15 , where the nonlinear quadratic characteristic is time dependent.

17. The method of claim 15 , where the act of applying the nonlinear quadratic characteristic results in an output signal, and where the act of applying the nonlinear quadratic characteristic is followed by band-pass filtering the output signal.

18. The method of claim 14 , where the act of generating the extended bandwidth acoustic signal comprises generating a weighted sum of the acoustic signal, the filtered upper bandwidth extension signal, and the lower bandwidth extension signal.

19. The method of claim 14 , where the lower bandwidth extension signal is weighted with a factor that is a function of an estimated signal-to-noise ratio of the acoustic signal.

20. A non-transitory computer readable medium encoded with computer executable instructions that, when loaded into memory associated with a suitably configured digital controller in a digital device, causes the device to perform a method for providing increased bandwidth, in a digitally sampled acoustic speech signal having a restricted bandwidth, so as to improve intelligibility of the speech signal, the method comprising:

using a digital-controller-implemented spectral shifter, coupled to the speech signal to generate digitally an upper bandwidth extension signal in which at least a portion of the speech signal is shifted upwardly by a predetermined shifting frequency value, and wherein the spectral shifter is configured to perform a cosine modulation of the speech signal;

using a first digital-controller-implemented high pass filter, coupled to an output of the spectral shifter, so as to digitally generate a filtered upper bandwidth extension signal by filtering the upper bandwidth extension signal to remove frequency components below a cutoff frequency;

using a second digital-controller-implemented high pass filter, disposed between the speech signal and the spectral shifter, to remove frequency components to the spectral shifter that are below a shifter input cutoff frequency; and

generating an extended bandwidth speech signal based on the speech signal and the filtered upper bandwidth extension signal.

Assignments (8)