MDCT domain post-filtering apparatus and method for quality enhancement of speech
First Claim
1. A post-filter apparatus for speech enhancement in a Modified Discrete Cosine Transform (MDCT) domain, comprising:
- a spectrum coefficient producer configured to produce a spectrum coefficient based on an MDCT coefficient of a current speech frame and an MDCT coefficient of a previous speech frame;
a normalizer configured to normalize the produced spectrum coefficient;
a transformer configured to transform the spectrum coefficient by mapping the normalized spectrum coefficient to a convex function;
a filter coefficient producer configured to produce a filter coefficient while adjusting a reflection degree of the transformed spectrum coefficient;
an MDCT coefficient producer configured to produce a new MDCT coefficient by multiplying the produced filter coefficient by the MDCT coefficient of the current speech frame; and
an inverse transformer transforming the new MDCT coefficient into a speech signal.
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Abstract
A post-filtering apparatus and method for speech enhancement in a modified discrete cosine transform (MDCT) domain are disclosed. In the apparatus and method, previous and current MDCT coefficients are used for obtaining a speech spectrum coefficient similar to a real speech spectrum, and a convex function is used for transforming the speech spectrum coefficient and obtaining a post-filter coefficient so that difference can increase in the case where the speech spectrum coefficient is small but decrease in the case where the coefficient is large. Then, the post-filter coefficient is applied to the MDCT coefficient. With this configuration, both the current and previous MDCT values are used, so that it is possible to obtain a spectrum coefficient similar to the real speech spectrum and to obtain a more accurate filter coefficient. Further, the coefficient is adaptively transformed through the convex function, thereby enhancing speech quality.
24 Citations
13 Claims
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1. A post-filter apparatus for speech enhancement in a Modified Discrete Cosine Transform (MDCT) domain, comprising:
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a spectrum coefficient producer configured to produce a spectrum coefficient based on an MDCT coefficient of a current speech frame and an MDCT coefficient of a previous speech frame; a normalizer configured to normalize the produced spectrum coefficient; a transformer configured to transform the spectrum coefficient by mapping the normalized spectrum coefficient to a convex function; a filter coefficient producer configured to produce a filter coefficient while adjusting a reflection degree of the transformed spectrum coefficient; an MDCT coefficient producer configured to produce a new MDCT coefficient by multiplying the produced filter coefficient by the MDCT coefficient of the current speech frame; and an inverse transformer transforming the new MDCT coefficient into a speech signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A post-filtering method for speech enhancement in a Modified Discrete Cosine Transform (MDCT) domain, comprising:
- performing, by a processor, operations of;
producing a spectrum coefficient based on an MDCT coefficient of a current speech frame, which MDCT coefficient of the current speech frame is loaded from a memory, and an MDCT coefficient of a previous speech frame; normalizing the produced spectrum coefficient; transforming the spectrum coefficient by mapping the normalized spectrum coefficient to a convex function; producing a filter coefficient while adjusting a reflection degree of the transformed spectrum coefficient; producing a new MDCT coefficient by multiplying the produced filter coefficient by the MDCT coefficient of the current speech frame; and transforming the new MDCT coefficient into a speech signal. - View Dependent Claims (9, 10, 11, 12, 13)
- performing, by a processor, operations of;
Specification