Method and apparatus for reducing noise in speech and audio signals
First Claim
1. A method for enhancing, within a signal bandwidth, a corrupted audio-frequency signal having a signal component and a noise component, the method comprising:
- analyzing the corrupted signal into plural sub-band signals, each occupying a frequency sub-band smaller than the signal bandwidth;
applying a respective signal gain function to the sub-band signal corresponding to each sub-band, thereby to yield respective gain-modified signals; and
synthesizing the gain-modified signals into an enhanced signal of the signal bandwidth;
wherein;
(a) within each frequency sub-band, the step of applying a respective signal gain function to a corresponding sub-band signal comprises evaluating a function that is preferentially sensitive to energy in the signal component;
(b) within each frequency sub-band, said applying step further comprises applying gain values to the corresponding sub-band signal, wherein said gain values are related to said preferentially sensitive function; and
(c) the step of evaluating the preferentially sensitive function comprises measuring a relative amount of speech energy within the corresponding sub-band, and measuring a relative amount of speech energy within a frequency range greater than, but centered on, the corresponding sub-band.
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Abstract
A method and apparatus are disclosed for enhancing, within a signal bandwidth, a corrupted audio-frequency signal. The signal which is to be enhanced is analyzed into plural sub-band signals, each occupying a frequency sub-band smaller than the signal bandwidth. A respective signal gain function is applied to each sub-band signal, and the respective sub-band signals are then synthesized into an enhanced signal of the signal bandwidth. The signal gain function is derived, in part, by measuring speech energy and noise energy, and from these determining a relative amount of speech energy, within the corresponding sub-band. In certain embodiments of the invention, the signal gain function is also derived, in part, by determining a relative amount of speech energy within a frequency range greater than, but centered on, the corresponding sub-band. In other embodiments of the invention, the sub-band noise energy is determined from a noise estimate that is updated at periodic intervals, but is not updated if the newest sample of the signal to be enhanced exceeds the current noise estimate by a multiplicative threshold (i.e., a threshold expressible in decibels). In still other embodiments of the invention, the value of the noise estimate is limited by an upper bound that is matched to the dynamic range of the signal to be enhanced.
68 Citations
12 Claims
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1. A method for enhancing, within a signal bandwidth, a corrupted audio-frequency signal having a signal component and a noise component, the method comprising:
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analyzing the corrupted signal into plural sub-band signals, each occupying a frequency sub-band smaller than the signal bandwidth; applying a respective signal gain function to the sub-band signal corresponding to each sub-band, thereby to yield respective gain-modified signals; and synthesizing the gain-modified signals into an enhanced signal of the signal bandwidth;
wherein;(a) within each frequency sub-band, the step of applying a respective signal gain function to a corresponding sub-band signal comprises evaluating a function that is preferentially sensitive to energy in the signal component; (b) within each frequency sub-band, said applying step further comprises applying gain values to the corresponding sub-band signal, wherein said gain values are related to said preferentially sensitive function; and (c) the step of evaluating the preferentially sensitive function comprises measuring a relative amount of speech energy within the corresponding sub-band, and measuring a relative amount of speech energy within a frequency range greater than, but centered on, the corresponding sub-band. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for enhancing, within a signal bandwidth, a corrupted audio-frequency signal having a signal component and a noise component, the method comprising:
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analyzing the corrupted signal into plural sub-band signals, each occupying a frequency sub-band smaller than the signal bandwidth; applying a respective signal gain function to the sub-band signal corresponding to each sub-band, thereby to yield respective gain-modified signals; and synthesizing the gain-modified signals into an enhanced signal of the signal bandwidth, wherein; (a) within each frequency sub-band, the step of applying a respective signal gain function to a corresponding sub-band signal comprises evaluating a function that is preferentially sensitive to energy in the signal component; (b) within each frequency sub-band, the step of applying further comprises applying gain values to the corresponding sub-band signal, wherein the gain values are related to the preferentially sensitive function; (c) the step of evaluating the preferentially sensitive function comprises; measuring speech energy; and measuring noise energy within the corresponding sub-band; (d) the step of measuring noise energy comprises evaluating a noise estimate in response to a recursive function of a sampled sub-band input is updated if a test is satisfied at sampled intervals (e) such that an update of a current noise estimate is generated if a new sample of the corrupted signal is less than a product of a multiplier and the current noise estimate, and is prevented if the new sample exceeds the product.
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12. A method for enhancing, within a signal bandwidth, a corrupted audio-frequency signal having a signal component and a noise component, the method comprising:
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analyzing the corrupted signal into plural sub-band signals, each occupying a frequency sub-band smaller than the signal bandwidth; applying a respective signal gain function to the sub-band signal corresponding to each sub-band, thereby to yield respective gain-modified signals; and synthesizing the gain-modified signals into an enhanced signal of the signal bandwidth, wherein; (a) within each frequency sub-band, the step of applying a respective signal gain function to a corresponding sub-band signal comprises evaluating a function that is preferentially sensitive to energy in the signal component; (b) within each frequency sub-band, the step of applying further comprises applying gain values to the corresponding sub-band signal, wherein the gain values are related to the preferentially sensitive function; (c) the step of evaluating the preferentially sensitive function comprises; measuring speech energy; and measuring noise energy within the corresponding sub-band; (d) the step of measuring noise energy comprises evaluating a noise estimate in response to a recursive function that is updated at least at sample intervals; (e) the value of the noise estimate is limited by an upper bound that is matched to the dynamic range of the corrupted signal to be enhanced; and (f) the gain values are derived from one or more ratios of a sub-band signal estimate to a sub-band signal noise estimate.
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Specification