Noise reducing method, noise reducing apparatus and telephone set
First Claim
1. A method for reducing noise contained in an input speech signal comprising steps of:
- detecting a level of a noise component in the input speech signal and forming a control signal based on the detected noise level; and
modifying steps taken in performing a noise reducing operation on the input speech signal for carrying out a modified noise reducing operation based on the control signal,wherein the noise reducing operation includes carrying out level expansion to produce different effects with a predetermined threshold value of an input speech signal level as a boundary, modifying the threshold value based on the control signal, and diminishing the level expansion effect when the input speech signal level is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a graph of an output speech signal level as ordinate data as a function of the input speech signal level as abcissa data shows a greater slope above the threshold value and a relatively lesser slope below the threshold value.
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Abstract
A noise reducing method and device for reducing the noise contained in an input speech signal collects the speech signal with a microphone 11 and converts the speech signal into a digital input signal x(n) with an A/D converter 12. A frame power calculating circuit 13 calculates a mean frame power rms for each frame of the digital input signal x(n). A suppression ratio calculating circuit 14 calculates different values of the noise suppression ratio depending on the magnitude of the mean frame power rms relative to pre-set threshold values. A level discrimination circuit 18 forms a changeover control signal depending on the noise level and transmits the changeover control signal to the suppression ratio calculating circuit 14 for switching control of the threshold value. The suppression ratio value from the suppression value calculating circuit 14 is transmitted via a smoothing circuit 15 to a noise-reducing circuit 16 and multiplied with the input signal x(n) for reducing the noise component of the speech signal. The effect of the noise-reducing operation is changed in response to the noise level and the intensity of the noise-reducing operation is moderated in portions having a low noise level to prevent deterioration in the sound quality.
51 Citations
17 Claims
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1. A method for reducing noise contained in an input speech signal comprising steps of:
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detecting a level of a noise component in the input speech signal and forming a control signal based on the detected noise level; and modifying steps taken in performing a noise reducing operation on the input speech signal for carrying out a modified noise reducing operation based on the control signal, wherein the noise reducing operation includes carrying out level expansion to produce different effects with a predetermined threshold value of an input speech signal level as a boundary, modifying the threshold value based on the control signal, and diminishing the level expansion effect when the input speech signal level is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a graph of an output speech signal level as ordinate data as a function of the input speech signal level as abcissa data shows a greater slope above the threshold value and a relatively lesser slope below the threshold value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for reducing noise in an input speech signal having a microphone for receiving the input speech signal and noise reducing means for reducing noise contained in the input speech signal received by the microphone, the apparatus comprising:
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noise level detection means for detecting a level of a noise component in the input speech signal and outputting a control signal based on the detected noise level; modifying means for modifying steps performed in a noise reducing operation for the input speech signal based on the control signal; speech level detection means for detecting a level of the input speech signal, whereby the noise reducing means carries out level expansion to give different effects with a predetermined threshold value of the input speech signal level as a boundary and modifies the threshold value responsive to the control signal; and means for diminishing the level expansion effect for the input speech signal when the level detected by the speech level detection means is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a slope of a curve of an output speech signal level plotted as a function of the input speech signal level is greater above the threshold value and is relatively less below the threshold value. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A telephone apparatus having a microphone to which a speech signal is input, a noise reducing circuit for reducing noise contained in the speech signal input to the microphone and a transmitter for transmitting signals produced by the noise reducing circuit, the telephone apparatus comprising:
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noise level detecting means for detecting a level of the noise component in the input speech signal; means for generating and outputting a control signal based on the detected noise level; speech level detection means for detecting a level of the input speech signal, whereby the noise reducing means carries out level expansion to give different effects with a predetermined threshold value of the input speech signal level as a boundary and modifies the threshold value based on the control signal; and means for diminishing the level expansion effect of the input speech signal when the level detected by the speech level detection means is less than or equal to the threshold value such that the level expansion effect for an input speech signal level above the threshold value is greater than the level expansion effect for an input speech signal level below the threshold value and a slope of a curve of an output speech signal level plotted as a function of the input speech signal level is greater above the threshold value and is less below the threshold value.
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Specification