Audio signal encoder and audio signal decoder

An audio signal encoder which encodes a mixed signal into which a plurality of pre-mixing audio signals have been mixed, said encoder comprising:

• a processor;
• a mixed signal generating unit configured to generate, using said processor, the mixed signal representing at least one audio signal having less than the plurality of pre-mixing audio signals by mixing the plurality of pre-mixing audio signals;
• a supplementary information generating unit configured to generate supplementary information including linear prediction coefficients for calculating, from at least one of the plurality of pre-mixing audio signals, a no-correlation signal representing, as a function of the mixed signal, a reference signal that is one of the plurality of pre-mixing audio signals, and (ii) a flag indicating a degree of correlation between the plurality of pre-mixing audio signals, wherein, in a case where the flag indicates that the plurality of pre-mixing audio signals have a low correlation, the supplementary information indicates that a plurality of audio signals, which are acoustically approximate to the plurality of pre-mixing audio signals other than the reference signal, are generated from the mixed signal by removing the calculated no-correlation signal from the mixed signal;
• a coding unit configured to code the mixed signal;
• and
• a coded stream generating unit configured to generate a first coded stream including the coded mixed signal and the generated supplementary information.

An audio signal decoding method for decoding a first coded stream and outputting audio signals, comprising:

• extracting, using a processor, a second coded stream, from the first coded stream, representing at least one mixed signal having less than a plurality of pre-mixing audio signals mixed into the mixed signal;
• extracting, from the first coded stream, supplementary information for reverting the mixed signal back to the plurality of pre-mixing audio signals, the supplementary information including (i) linear prediction coefficients for representing at least one of the plurality of pre-mixing audio signals as a function of the mixed signal, and (ii) a flag indicating a degree of correlation between the plurality of pre-mixing audio signals;
• decoding the second coded stream representing the mixed signal;
• calculating a no-correlation signal representing, as a function of the mixed signal, a reference signal that is one of the plurality of pre-mixing audio signals by using the linear prediction coefficients in the supplementary information in a case where the flag included in the supplementary information indicates that the plurality of pre-mixing audio signals have a low correlation,
• separating the mixed signal generated by said decoding by removing the no-correlation signal from the mixed signal, and generating a plurality of audio signals which are acoustically approximate to the plurality of pre-mixing audio signals other than the reference signal;
• and
• reproducing the decoded mixed signal or the plurality of audio signals separated from the mixed signal.

A non-transitory computer-readable recording medium having stored thereon a program for use in an audio signal decoder which decodes a first coded stream and outputs audio signals, wherein when executed, said program causes a computer to perform a method comprising:

• extracting, from the first coded stream, a second coded stream representing at least one mixed signal having less than a plurality of pre-mixing audio signals mixed into the mixed signal;
• extracting, from the inputted first coded stream, supplementary information for reverting the mixed signal back to the plurality of pre-mixing audio signals, the supplementary information including (i) linear prediction coefficients for representing at least one of the plurality of pre-mixing audio signals as a function of the mixed signal, and (ii) a flag indicating a degree of correlation between the plurality of pre-mixing audio signals;
• decoding the second coded stream representing the mixed signal;
• calculating a no-correlation signal representing, as a function of the mixed signal, a reference signal that is one of the plurality of pre-mixing signals by using the linear prediction coefficients in the supplementary information in a case where the flag included in the supplementary information indicates that the plurality of pre-mixing audio signals have a low correlation,
• separating the mixed signal generated by said decoding by removing the no-correlation signal from the mixed signal, and generating a plurality of audio signals which are acoustically approximate to the plurality of pre-mixing audio signals other than the reference signal;
• and
• reproducing the decoded mixed signal or the plurality of audio signals separated from the mixed signal.