Method and apparatus of postfiltering using a first spectrum parameter of an encoded sound signal and a second spectrum parameter of a lesser degree than the first spectrum parameter

A postfilter for reproducing a sound signal that has been encoded with an encoder, by using a decoder and compensating a reproduced signal that was output from said decoder, said postfilter comprising:

• means for converting a first linear predictive coefficient supplied from said encoder to preset k parameters, said first linear predictive coefficient being related to said sound signal encoded by said encoder;
• means for extracting an arbitrary k parameter from among said k parameters;
• means for converting said extracted k parameter to a second linear predictive coefficient, wherein the degree of said second linear predictive coefficient is lower than that of said first linear predictive coefficient;
• a spectrum postfilter for generating a first transfer function of autoregressive moving average type having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, said spectrum postfilter receiving said reproduced signal output from said decoder and filtering said reproduced signal based on said first transfer function;
• means for calculating an impulse response of said spectrum postfilter based on said first linear predictive coefficient and said second linear predictive coefficient;
• means for calculating a preset autocorrelation function based on said calculated impulse response;
• means for calculating said compensation coefficient based on said calculated autocorrelation function;
• and
• a compensation filter for generating a second transfer function based on said compensation coefficient and filtering an output of said spectrum postfilter based on said second transfer function,
• wherein an output of said compensation filter that corresponds to a filtered reproduced signal is a reproduction of said sound signal.

A postfilter for reproducing a sound signal that has been encoded with an encoder, by using a decoder and compensating a reproduced signal that was output from said decoder, said postfilter comprising:

• means for calculating a first linear predictive coefficient in accordance with said reproduced signal received from said decoder;
• means for converting a first linear predictive coefficient to preset k parameters;
• means for extracting an arbitrary k parameter from among said k parameters;
• means for converting said extracted k parameter to a second linear predictive coefficient, wherein the degree of said second linear predictive coefficient is lower than that of said first linear predictive coefficient;
• a spectrum postfilter for generating a first transfer function of autoregressive moving average type having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, said spectrum postfilter receiving said reproduced signal output from said decoder and filtering said reproduced signal based on said first transfer function;
• means for calculating an impulse response of said spectrum postfilter based on said first linear predictive coefficient and said second linear predictive coefficient;
• means for calculating a preset autocorrelation function based on said calculated impulse response;
• means for calculating said compensation coefficient based on said calculated autocorrelation function;
• and
• a compensation filter for generating a second transfer function based on said compensation coefficient and filtering an output of said spectrum postfilter based on said second transfer function,
• wherein an output of said compensation filter that corresponds to a filtered reproduced signal is a reproduction of said sound signal.

A method of postfiltering for reproducing a sound signal that has been encoded with an encoder, by using a decoder and postfiltering a reproduced signal that was output from said decoder, said method of postfiltering comprising the steps of:

• sampling a preset sampling number of first spectrum parameter output from said encoder, said first spectrum parameter being related to said sound signal;
• sampling a preset sampling number of said reproduced signal;
• calculating a second spectrum parameter of which degree is lower than that of said sampled first spectrum parameter;
• first filtering for generating a first transfer function having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, and filtering said sampled reproduced signal output from said decoder based on said first transfer function;
• adaptively calculating a compensation coefficient based on said sampled first spectrum parameter and said second spectrum parameter;
• and
• second filtering for generating a second transfer function based on said compensation coefficient and filtering a signal filtered in said first filtering step based on said second transfer function to obtain a re-filtered signal,
• wherein said re-filtered signal corresponds to a reproduction of said sound signal.