Patent ID: 8725501

Claim:
A speech decoding apparatus configured as a circuit comprising: an adaptive codebook that generates an excitation signal; an average amplitude calculator that calculates an average amplitude for one pitch period from an end of the excitation signal stored in the adaptive codebook; a memory that holds the calculated average amplitude; an energy change rate calculator that calculates a ratio of a first average amplitude and a second average amplitude as an energy change rate, and smoothes the energy change rate over time, the first average amplitude being calculated by the average amplitude calculator with resect to a resent calculation target period the second average amplitude being calculated by the average amplitude calculator with respect to a calculation reference period earlier than the present calculation target period, and the second average amplitude being stored in the memory; a decider that decides to set one of the smoothed energy change rate acquired in the energy change rate calculator and an adaptive codebook gain decoded before the present calculation target period as an adaptive codebook gain for processing a generator that generates a signal for a lost frame by multiplying the excitation signal by the adaptive codebook gain for processing set by the decider with respect to the lost frame; and a noise applier that applies noise to a high-frequency band of the generated signal, wherein the noise applier determines voiced stationarity based at least on whether fluctuation of a decoding pitch period before the lost frame is large or small, and sets the high-frequency band as a frequency band to apply noise to when the voiced stationarity is determined to be low, or limits the frequency band to apply noise to, to a higher frequency part in the high-frequency band, when the voiced stationarity is determined to be high.