Noise reduction method and system

1. A noise reduction method for reducing unwanted sounds in signals received from an arrangement of microphones including the steps of:

sensing sound sources distributed around a specified target direction by way of an arrangement of microphones to produce left and right microphone output signals including high frequency signals and low frequency signals;

determining the magnitude or power of the left and right microphone signals;

attenuating the signals either i) for both high frequency signals and low frequency signals or ii) for high frequency signals alone, based on the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals, and

additionally attenuating the signals for low frequencies based on the magnitude or power of the difference between the left and right microphone signals or a value derived from the magnitude or power of the difference between the left and right microphone signals.

2. A method according to claim 1 further including the steps of:

determining the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals,

wherein each of the attenuating steps is further based on a comparison of the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals with the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

3. A method according to claim 2 further comprising the step of time-averaging the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

4. A method according to claim 1 wherein each of the attenuating steps is based on the ratio of the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals to the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

5. A method according to claim 4 wherein each of the attenuating steps is based on one minus the ratio.

6. A method according to claim 4 wherein each of the attenuating steps is based on a transformation of the ratio.

7. A method according to claim 6 wherein each of the attenuating steps is based on one minus the transformation of the ratio.

8. A method according to claim 1 further comprising the step of time-averaging the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

9. A method according to claim 8 wherein the step of time-averaging includes time-averaging utilizing asymmetric rise and fall times.

10. A method to claim 1 wherein the attenuated signals are scaled by a function.

11. A method to claim 1 further comprising eliminating unwanted reduction of target output level in high noise levels through an estimator of the amount of noise being eliminated.

12. A method according to claim 11 wherein the estimator of the amount of noise being eliminated over a frequency range of interest is derived from the maximum attenuation applied across that range.

13. A system for reducing unwanted sounds in signals received from an arrangement of microphones including:

sensing means for sound sources distributed around a specified target direction by way of an arrangement of microphones to produce left and right microphone output signals including high frequency signals and low frequency signals;

determination means for determining the magnitude or power of the left and right microphone signals;

first attenuation means for attenuating either i) high frequency signals and low frequency signals or ii) high frequency signals alone, based on the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals; and

second attenuation means for additionally attenuating the low frequency signals based on the magnitude or power of the difference between the left and right microphone signals or a value derived from the magnitude or power of the difference between the left and right microphone signals.

14. A system according to claim 13 wherein the determination means is further arranged to determine the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals; and

each of the first and second attenuation means is further arranged to attenuate the signals based on a comparison of the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals with the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

15. A system according to claim 13 wherein each of the first and second attenuation means is arranged to attenuate the signals based on the ratio of the difference of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals to the sum of the magnitudes or powers or values derived from the magnitudes or powers of the left and right microphone signals.

16. A system according to claim 15 wherein each of the first and second attenuation means is arranged to attenuate the signals based on one minus the ratio.

17. A system according to claim 15 wherein each of the first and second attenuation means is arranged to attenuate the signals based on a transformation of the ratio.

18. A system according to claim 17 wherein each of the first and second attenuation means is arranged to attenuate the signals based on one minus the transformation of the ratio.