Patent ID: 7472056

Claim:
A transcoder for converting an input Code-Excited Linear Prediction (CELP) codec stream of one format into an output CELP codec stream of another format, comprising: a decoding unit of an input CELP codec, which converts a bitstream encoded in an input CELP codec format into a speech signal; a transcoding filter, which performs filtering of the speech signal decoded in the decoding unit of the input CELP codec with filter characteristics calculated by adapting an optimum weight to minimize spectral distortion based on a reference filter; a transcoding filter design unit, which extracts the optimum weight to minimize spectral distortion of the transcoding filter from a weight set, and then supplies the optimum weight to the transcoding filter, the transcoding filter design unit to: randomly select one weight pair from a weight set; evaluate the transcoding filter by applying the selected weight pair to the transcoding filter having a perceptual weighting filter form; calculate a frequency response of the evaluated transcoding filter; calculate a spectral distortion of the transcoding filter by comparing the frequency response of the reference filter with the calculated frequency response; calculate the spectral distortion corresponding to each weight pair by evaluating the transcoding filter by applying the selected weight pair to the transcoding filter having a perceptual weighting filter form, calculating the frequency response of the evaluated transcoding filter, and calculating the spectral distortion of the transcoding filter by comparing the frequency response of the reference filter with the calculated frequency response, for every weight pair from the weight set; and selecting a weight pair resulting in a minimum spectral distortion as the optimum weight; and an encoding unit of an output CELP codec, which generates a bitstream in an output CELP codec format by encoding the speech signal filtered in the transcoding filter.