Method and apparatus for suppressing audible noise in speech transmission
First Claim
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1. A method of suppressing audible noise during transmission of a speech signal by means of a multi-layer self-organizing feed-back neural network, the method comprising the steps of:
- providing a minima detection layer, a reaction layer, and a diffusion layer, and an integration layer, the minima detection layer for tracking a plurality of minima, the reaction layer utilizing a non-linear reaction function, the diffusion layer having only local coupling of neighboring nodes within the diffusion layer, and the integration layer summing a nodal output of the diffusion layer into a single node without weighting; and
defining a filter function F(f,T) for noise filtering by successively coupling nodes between the minima detection layer, the reaction layer, the diffusion layer, and the integration layer, wherein f denotes a frequency of a spectral component being analysed at time T.
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Abstract
Method of suppressing audible noise in speech transmission by means of a multi-layer self-organizing fed-back neural network comprising a minima detection layer, a reaction layer, a diffusion layer and an integration layer, said layers defining a filter function F(f,T) for noise filtering.
47 Citations
13 Claims
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1. A method of suppressing audible noise during transmission of a speech signal by means of a multi-layer self-organizing feed-back neural network, the method comprising the steps of:
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providing a minima detection layer, a reaction layer, and a diffusion layer, and an integration layer, the minima detection layer for tracking a plurality of minima, the reaction layer utilizing a non-linear reaction function, the diffusion layer having only local coupling of neighboring nodes within the diffusion layer, and the integration layer summing a nodal output of the diffusion layer into a single node without weighting; and
defining a filter function F(f,T) for noise filtering by successively coupling nodes between the minima detection layer, the reaction layer, the diffusion layer, and the integration layer, wherein f denotes a frequency of a spectral component being analysed at time T. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
using a neural network to generate the filter function F(f,T) from a spectrum A(f,T) being derived by Fourier transformation from a frame of an input signal x(t);
spectrum A(f,T), and the filter function F(f,T) being multiplied to generate a noise-reduced spectrum B(f,T) that, by application of an inverse Fourier transformation in a synthesis unit (12), generates a noise reduced speech signal y(t),wherein one node of the minima detection layer operates independently from other nodes of the minima detection layer to process a single signal component of the frequency f, and wherein t denotes the time of handling a sample of the signals x and/or y.
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6. The method as in claim 1, further comprising the step of evaluating spectral properties of speech signals in the diffusion layer, the nodes of said diffusion layer effecting frequency component coupling in a manner of diffusion in a frequency domain, with a diffusion constant D>
- 0.
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7. The method as in claim 1, further comprising the step of multiplying all frequency components of filter function F(f,T) at time T with corresponding amplitudes A(f,T), wherein the integration layer effects integration over frequency components of the filter function F(f,T) to produce an integration signal S(T) to be fed back into the reaction layer.
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8. The method as in claim 1,
wherein signal components of the speech speech are modulated within modulation frequencies between 0.6 Hz and 6 Hz, an attenuation is less than 3 dB for all values of control parameter K in order to pass the filter function F(f,T) in an optimum manner, the modulation frequencies between 0.6 Hz and 6 Hz corresponding to modulation of human speech, and wherein the signal components outside of the range of 0.6 Hz to 6 Hz are identified as noise, and are more strongly attenuated based on a value of an adjustable parameter K.
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9. An apparatus for audible noise suppression during transmission of a speech signal with a neural network comprising:
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a minima detection layer, a reaction layer, a diffusion layer, and an integration layer;
the minima detection layer for tracking a plurality of minima, the reaction layer utilizing a non-linear reaction function, the diffusion layer having only local coupling of neighboring nodes within the diffusion layer, and the integration layer for summing a nodal output of the diffusion layer into a single node without weighting; and
a filter function F(f,T) for noise filtering, wherein frequency components of a spectrum differ by frequency f and correspond to unique nodes for each of the layers of the network, except for the integration layer, and wherein each node of the minima detection layer derives a value M(f,T) for the frequency component f at time T, where M(f,T) is obtained by time-averaging an amplitude A(f,T) over a time interval of a length of m frames and a minimum detection of said average within a time interval of the length of 1 frames, with 1>
m.- View Dependent Claims (10, 11, 12, 13)
wherein a range of values of the reaction function is limited to an interval [r1, r2], by a reaction function reading r(S)=(r2− - r1)exp(S)+r1,
wherein r1 and r2 are arbitrary numbers, and r1<
r2, andwherein the range of values of the resultant relative spectrum R(f,T) is limited to the interval [0, 1] by setting R(f,T)=1 in case R(f,T)>
1 and setting R(f,T)=0 in case R(f,T)<
0.
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12. The apparatus as in claim 10, wherein the nodes of the reaction layer have input thereto an integration signal S(T−
- 1) from a preceding frame (time T−
1), and are computed in the integration layer and are fed back into the reaction layer.
- 1) from a preceding frame (time T−
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13. The apparatus as in claim 9, wherein attenuation of the speech signal for all indicated values of control parameter K is lower than 3 dB when speech signals are modulated within modulation frequencies between 0.6 Hz and 6 Hz.
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