Sound signal decoding method, sound signal decoder, program, and recording medium

A sound signal decoding device for decoding an inputted code representing an encoded sound signal for each time frame to obtain a decoded sound signal having C channels (C is an integer of 2 or larger), the sound signal decoding device comprising a processor configured to execute operations comprising, as processing for a current frame:

• decoding a monaural code included in the inputted code by a decoding scheme that includes processing of applying a window having overlap between frames to obtain a monaural decoded sound signal, as processing for a current frame;
• decoding an additional code included in the inputted code to obtain an additional decoded signal, wherein the additional decoded signal represents a monaural decoded signal of a section corresponding to the overlap between the current frame and an immediately following frame (hereinafter referred to as “a section X”), as processing for the current frame;
• obtaining a decoded downmix signal, wherein the decoded downmix signal represents a concatenation of a part of the monaural decoded sound signal of a section except the section X (hereinafter referred to as “a section Y”) and the additional decoded signal for the section X;
• and
• obtaining and output the decoded sound signal having the C channels from a windowed signal of the decoded downmix signal by upmix processing using a characteristic parameter obtained from a stereo code included in the inputted code,
• thereby a first time delay caused by the stereo decoding of the frame is not longer than a second time delay caused by the monaural decoding.