System and method for generating an audio signal representing the speech of a user

1. A method of generating a signal representing the speech of a user, the method comprising:

obtaining a first audio signal representing the speech of the user using a sensor in contact with the user;

obtaining a second audio signal using an air conduction sensor, the second audio signal representing the speech of the user and including noise from the environment around the user;

detecting periods of speech in the first audio signal;

applying a speech enhancement algorithm to the second audio signal to reduce the noise in the second audio signal, the speech enhancement algorithm using the detected periods of speech in the first audio signal;

equalizing the first audio signal using the noise-reduced second audio signal to produce an output audio signal representing the speech of the user, the equalizing includes performing linear prediction analysis on both the first audio signal and the noise-reduced second audio signal to construct an equalization filter, wherein the performing linear prediction analysis further includes:

(i) estimating linear prediction coefficients for both the first audio signal and the noise-reduced second audio signal;

(ii) using the linear prediction coefficients for the first audio signal to produce an excitation signal for the first audio signal;

(iii) using the linear prediction coefficients for the noise-reduced second audio signal to construct a frequency domain envelope; and

(iv) equalizing the excitation signal for the first audio signal using the frequency domain envelope.

2. The method as claimed in claim 1 , wherein detecting periods of speech in the first audio signal comprises detecting parts of the first audio signal where the amplitude of the audio signal is above a threshold value.

3. The method as claimed in claim 1 , wherein applying a speech enhancement algorithm comprises applying spectral processing to the second audio signal.

4. The method as claimed in claim 1 , wherein applying a speech enhancement algorithm to reduce the noise in the second audio signal comprises using the detected periods of speech in the first audio signal to estimate the noise floors in the spectral domain of the second audio signal.

5. The method as claimed in claim 1 , wherein equalizing the first audio signal comprises (i) using long-term spectral methods to construct an equalization filter, or (ii) using the first audio signal as an input to an adaptive filter that minimizes the mean-square error between the filter output and the noise-reduced second audio signal.

6. The method as claimed in claim 1 , wherein prior to the step of equalizing, the method further comprises the step of applying a speech enhancement algorithm to the first audio signal to reduce the noise in the first audio signal, the speech enhancement algorithm making use of the detected periods of speech in the first audio signal, and wherein the step of equalizing comprises equalizing the noise-reduced first audio signal using the noise-reduced second audio signal to produce the output audio signal representing the speech of the user.

7. The method as claimed in claim 1 , further comprising:

obtaining a third audio signal using a second air conduction sensor, the third audio signal representing the speech of the user and including noise from the environment around the user; and

using a beamforming technique to combine the second audio signal and the third audio signal and produce a combined audio signal;

and wherein the step of applying a speech enhancement algorithm comprises applying the speech enhancement algorithm to the combined audio signal to reduce the noise in the combined audio signal, the speech enhancement algorithm using the detected periods of speech in the first audio signal.

8. The method as claimed in claim 1 , further comprising:

obtaining a fourth audio signal representing the speech of a user using a second sensor in contact with the user; and

using a beamforming technique to combine the first audio signal and the fourth audio signal and produce a second combined audio signal;

and wherein the step of detecting periods of speech comprises detecting periods of speech in the second combined audio signal.

9. A non-transitory computer readable medium carrying a computer program for controlling one or more processors to perform the method as claimed in claim 1 .

10. A device for use in generating an audio signal representing the speech of a user, the device comprising:

processing circuitry that is configured to:

receive a first audio signal representing the speech of the user from a sensor in contact with the user;

receive a second audio signal from an air conduction sensor, the second audio signal representing the speech of the user and including noise from the environment around the user;

detect periods of speech in the first audio signal;

apply a speech enhancement algorithm to the second audio signal to reduce the noise in the second audio signal, the speech enhancement algorithm using the detected periods of speech in the first audio signal; and

equalize the first audio signal using the noise-reduced second audio signal to produce an output audio signal representing the speech of the user;

wherein the processing circuitry is configured to equalize the first audio signal by performing linear prediction analysis on both the first audio signal and the noise-reduced second audio signal to construct an equalization filter, performing the linear prediction analysis including:

(i) estimating linear prediction coefficients for both the first audio signal and the noise reduced second audio signal;

(ii) using the linear prediction coefficients for the first audio signal to produce an excitation signal for the first audio signal;

(iii) using the linear prediction coefficients for the noise-reduced audio signal to construct a frequency domain envelope; and

(iv)equalizing the excitation signal for the first audio signal using the frequency domain envelope.

11. The device as claimed in claim 10 , the device further comprising:

a contact sensor that is configured to contact the body of the user when the device is in use and to produce the first audio signal; and

an air-conduction sensor that is configured to produce the second audio signal.

12. A device for generating an audio signal representing the speech of a user, the device comprising:

a processor configured to:

receive a first audio signal representing the speech of the user from a sensor in contact with the user;

receive a second audio signal representing the speech of the user including noise from an environment around the user;

detect periods of speech in the first audio signal;

apply a speech enhancement algorithm to the second audio signal to reduce the noise in the second audio signal; and

equalize the first audio signal using the noise-reduced second audio signal to produce and output an audio signal representing the speech of the user, the equalizing including:

(i) estimate linear prediction coefficients for both the first audio signal and the noise reduced second audio signal;

(ii) use the linear prediction coefficients for the first audio signal to produce an excitation signal for the first audio signal; and

(iii) use the linear prediction coefficients for the noise-reduced audio signal to construct a frequency domain envelope; and

(iv) equalize the excitation signal for the first audio signal using the frequency domain envelope.

13. The device as claimed in claim 12 , wherein the processor is further configured to:

perform linear prediction analysis on the first audio signal and the second audio signal to construct an equalization filter.

14. A device for generating an audio signal representing the speech of a user, the device comprising:

a processor configured to:

receive a first audio signal representing the speech of the user from a sensor in contact with the user;

receive a second audio signal representing the speech of the user including noise from an environment around the user;

detect periods of speech in the first audio signal;

apply a speech enhancement algorithm to the second audio signal to reduce the noise in the second audio signal, wherein the speech enhancement algorithm analyzes the first and noise-reduced second audio signals to generate an excitation signal for the first audio signal and a frequency domain envelope for the noise-reduced audio signal; and

equalize the excitation signal for the first audio signal using the frequency domain envelope and the noise-reduced second audio signal to produce and output an audio signal representing the speech of the user.

15. A device for generating an audio signal representing the speech of a user, the device comprising:

a processor configured to:

receive a first audio signal representing the speech of the user from a sensor in contact with the user;

receive a second audio signal representing the speech of the user including noise from an environment around the user;

detect periods of speech in the first audio signal;

apply a speech enhancement algorithm to the second audio signal to reduce the noise in the second audio signal;

equalize the first audio signal using the noise-reduced second audio signal to produce and output an audio signal representing the speech of the user; and

analyze the first and noise-reduced second audio signals by estimating linear prediction coefficients for the first and noise-reduced second audio signals, the linear prediction coefficients being used to generate the excitation signal and the frequency domain envelope.