Encoding device, decoding device, encoding method, decoding method, encoding program, decoding program, and recording medium

This invention provides an encoding device and a decoding device that make it possible, with a small encoded size, to reproduce a frequency-domain envelope sequence that exhibits good approximation precision in the vicinity of a peak due to the pitch period of an audio signal. This encoding device has a periodic-combined-envelope generation unit and a variable-length-encoding unit. Said periodic-combined-envelope generation unit generates a periodic combined-envelope sequence, said periodic combined-envelope sequence being a frequency-domain sequence based on the following: a spectral-envelope sequence, said spectral-envelope sequence being a frequency-domain sequence corresponding to linear-prediction-coefficient symbols obtained from an input audio signal; and a frequency-domain period. The variable-length-encoding unit encodes a frequency-domain sequence derived from the input audio signal. This decoding device has a periodic-combined-envelope generation unit and a variable-length-decoding unit. Said periodic-combined-envelope generation unit generates a periodic combined-envelope sequence, said periodic combined-envelope sequence being a frequency-domain sequence based on the following: a spectral-envelope sequence, said spectral-envelope sequence being a frequency-domain sequence corresponding to the abovementioned linear-prediction-coefficient symbols; and the abovementioned frequency-domain period. The variable-length-decoding unit decodes a variable-length code, yielding a frequency-domain sequence.