Noise suppressing device, noise suppressing method, and a non-transitory computer-readable recording medium storing noise suppressing program

1. A noise suppressing device for suppress a noise component included in an input signal, the noise suppressing device comprising:

a processor; and

a non-transitory storage medium containing program instructions, execution of which by the processor causes the noise suppressing device to provide functions of

a noise estimating unit configured to estimate a noise spectrum based on an input spectrum obtained by performing a frequency analysis on the input signal;

a speech-likelihood calculating unit configured to calculate speech-likelihood based on the input spectrum and the noise spectrum;

a suppression-gain calculating unit configured to calculate first suppression gain based on the input spectrum and the noise spectrum;

a suppression-gain combining unit configured to calculate third suppression gain by combining the first suppression gain and second suppression gain, which is provided as a predetermined constant value or provided by smoothing the first suppression gain, based on the speech-likelihood; and

a multiplying unit obtaining an output spectrum by multiplying the input spectrum by the third suppression gain.

2. The noise suppressing device according to claim 1 , wherein the speech-likelihood calculating unit calculates the speech-likelihood for each frequency band.

3. The noise suppressing device according to claim 1 , wherein the execution of the program instructions by the processor causes the noise suppressing device to further provide functions of:

a speech-to-noise-ratio calculating unit configured to calculate a speech-to-noise-ratio based on power of the input spectrum and power of the noise spectrum; and

a speech-to-noise-ratio smoothing unit configured to calculate a smoothed speech-to-noise-ratio by smoothing the speech-to-noise-ratio along both a frequency-axis direction and a time-axis direction, wherein the speech-likelihood calculating unit calculates the speech-likelihood based on the smoothed speech-to-noise-ratio.

4. The noise suppressing device according to claim 3 , wherein the speech-likelihood calculating unit converts the smoothed speech-to-noise-ratio into the speech-likelihood by using a predetermined weakly-monotonically-increasing nonlinear function.

5. The noise suppressing device according to claim 4 , wherein in the predetermined weakly-monotonically-increasing nonlinear function, a range of the speech-likelihood is between 0 and 1.

6. The noise suppressing device according to claim 1 , wherein the suppression-gain combining unit adds a value, which is obtained by multiplying the first suppression gain by the speech-likelihood, to a value, which is obtained by multiplying the second suppression gain by a value obtained by subtracting the speech-likelihood from 1, so as to calculate the third suppression gain.

7. The noise suppressing device according to claim 1 , wherein the execution of the program instructions by the processor causes the noise suppressing device to further provide functions of:

a suppression-gain smoothing unit configured to calculate the second suppression gain by smoothing the first suppression gain along both a frequency-axis direction and a time-axis direction.

8. A noise suppressing method for suppressing a noise component included in an input signal, the noise suppressing method comprising:

causing a noise estimating unit to estimate a noise spectrum based on an input spectrum obtained by performing a frequency analysis on the input signal;

causing a speech-likelihood calculating unit to calculate speech-likelihood based on the input spectrum and the noise spectrum;

causing a suppression-gain calculating unit to calculate first suppression gain based on the input spectrum and the noise spectrum;

causing a suppression-gain combining unit to calculate third suppression gain by combining the first suppression gain and second suppression gain, which is provided as a predetermined constant value or provided by smoothing the first suppression gain, based on the speech-likelihood; and

causing a multiplying unit to obtain an output spectrum by multiplying the input spectrum by the third suppression gain.

9. A non-transitory computer-readable recording medium storing a noise suppressing program for suppressing a noise component included in an input signal, the noise suppressing program containing program instructions for causing a computer to perform steps of:

estimating a noise spectrum based on an input spectrum obtained by performing a frequency analysis on the input signal;

calculating speech-likelihood based on the input spectrum and the noise spectrum;

calculating first suppression gain based on the input spectrum and the noise spectrum;

calculating third suppression gain by combining the first suppression gain and second suppression gain, which is provided as a predetermined constant value or provided by smoothing the first suppression gain, based on the speech-likelihood; and

obtaining an output spectrum by multiplying the input spectrum by the third suppression gain.