A sound signal receiving and decoding method to be performed by a terminal apparatus connected to a first communication line and a second communication line with a lower priority level than the first communication line, the method being characterized by comprising: a reception step (S221) of, for each frame, if an extended code with the same frame number as a monaural code included in a first code string input from the first communication line is included in extended codes included in a second code string input from the second communication line, outputting the monaural code included in the first code string input from the first communication line and the extended code with the same frame number as the monaural code, and if an extended code with the same frame number as the monaural code included in the first code string input from the first communication line is not included in the extended codes included in the second code string input from the second communication line, outputting the monaural code included in the first code string input from the first communication line and an extended code with the closest frame number to that of the monaural code among the extended codes included in the second code string input from the second communication line; and a decoding step (S222) of, for each frame, obtaining and outputting decoded digital sound signals of C, C being an integer that is at least 2, channels based on the monaural code output in the reception step (S221) and the extended code output in the reception step (S221), and the extended code is a code indicating a feature parameter which is a parameter that indicates a feature of a difference between the input digital sound signals of C channels and has a low temporal resolution. a reception step (S221) of, for each frame, if an extended code with the same frame number as a monaural code included in a first code string input from the first communication line is included in extended codes included in a second code string input from the second communication line, outputting the monaural code included in the first code string input from the first communication line and the extended code with the same frame number as the monaural code, and if an extended code with the same frame number as the monaural code included in the first code string input from the first communication line is not included in the extended codes included in the second code string input from the second communication line, outputting the monaural code included in the first code string input from the first communication line and an extended code with the closest frame number to that of the monaural code among the extended codes included in the second code string input from the second communication line; and a decoding step (S222) of, for each frame, obtaining and outputting decoded digital sound signals of C, C being an integer that is at least 2, channels based on the monaural code output in the reception step (S221) and the extended code output in the reception step (S221), and the extended code is a code indicating a feature parameter which is a parameter that indicates a feature of a difference between the input digital sound signals of C channels and has a low temporal resolution. <EOS>