Patent ID: 8117028
Filing Date: 2012-02-14
Classification: G10L

Abstract:
1. A code-conversion apparatus, comprising: a digital signal processor, the digital signal processor comprising: a code-demultiplexing module which demultiplexes multiplexed codes; and a code-multiplexing module which multiplexes codes, wherein code string data resulted from multiplexing codes obtained by encoding an audio signal in accordance with a first encoding process is demultiplexed into codes in said code-demultiplexing module, the thus demultiplexed codes are converted into codes which are in conformity to a second process different from said first process, the thus converted codes are transmitted to said code-multiplexing module, and the converted codes are multiplexed with one another in said code-multiplexing module to thereby generate code string data, characterized by an audio-decoding module which decodes excitation-signal information including an adaptive codebook code, a fixed codebook code and a gain code all of which are in conformity to said first process and which were demultiplexed in said code-demultiplexing module, and drives a synthesis filter having a first linear prediction coefficient decoded in accordance with said first process, with an excitation signal obtained from said excitation-signal information, based on a linear prediction coefficient code demultiplexed in said code-demultiplexing module, to thereby synthesize a decoded audio signal; a fixed codebook code generation module which obtains at least a part of a fixed codebook code which is in conformity to said second process, from a fixed codebook code which is in conformity to said first process, obtains a fixed codebook signal through the use of said decoded audio signal, and generates a fixed codebook code which is in conformity to said second process by combining a fixed codebook code associated with said fixed codebook signal with the partial fixed codebook code obtained by changing said code; a module which generates a first linear prediction coefficient decoded in accordance with said first process and a second linear prediction coefficient decoded in accordance with said second process based on said linear prediction coefficient code demultiplexed in said code-demultiplexing module; an adaptive codebook code conversion module which generates an adaptive codebook code which is in conformity to said second process by changing an adaptive codebook code which is in conformity to said first process and which is input from said code-demultiplexing module in accordance with the correspondence between codes in conformity to said first process and codes in conformity to said second process and transmits adaptive codebook delay corresponding to an adaptive codebook code in conformity to said second process to a later-mentioned target signal calculation circuit as second adaptive codebook delay; an impulse response calculation circuit which defines an auditory sense weighted synthesis filter through the use of said first and second linear prediction coefficients and outputs an impulse response signal of said auditory sense weighted synthesis filter; and a target signal calculation circuit which calculates a first target signal from said decoded audio signal and said first and second linear prediction coefficients, wherein said target signal calculation circuit further calculates a second adaptive codebook signal and an optimal adaptive codebook gain from: said second adaptive codebook signal, a second excitation signal generated in the past in accordance with a second fixed codebook signal and said gain signal, said impulse response signal, said first target signal, and said second adaptive codebook delay, and outputs said first target signal, said optimal adaptive codebook gain and said second adaptive codebook signal, wherein said fixed codebook code generation circuit generates a fixed codebook code which is in conformity to said second process with respect to a pulse to which a correspondence between said first and second processes can be applied by changing said first fixed codebook code in accordance with said correspondence by selecting such a pulse location and a pulse sign such that a distance between a fixed codebook signal and a second target signal is minimized with respect to a pulse to which said correspondence cannot be applied, wherein said fixed codebook signal being filtered through convolution operation of said fixed codebook signal and said impulse response signal, wherein said second target signal resulting from subtracting a signal obtained by multiplying said optimal adaptive codebook gain with a second adaptive codebook signal, wherein said second adaptive codebook signal filtered by a convolution of said second adaptive codebook signal and said impulse response signal from said first target signal, wherein said first target signal defines a fixed codebook signal from a pulse location and a pulse sign resulting from changing said first fixed codebook code and a pulse location and a pulse sign resulted from said selection as a second fixed codebook signal and outputs a code decodable in accordance with said second process and corresponding to said second fixed codebook signal as a second fixed codebook code.