AUDIO DEVICE, MISSING BAND ESTIMATION DEVICE, SIGNAL PROCESSING METHOD, AND FREQUENCY BAND ESTIMATION DEVICE

During high-frequency interpolation, a harmonic generation unit first generates a harmonic signal for an input compressed audio signal. An HPF unit, having a cutoff frequency, extracts a high frequency component from the compressed audio signal in parallel with the generation of the harmonic signal. An HPF unit, having a cutoff frequency, extracts a high frequency component from the compressed audio signal. An estimation unit estimates a missing band in the compressed audio signal on the basis of a ratio of the signal level of a difference signal to the signal level of an output signal, the difference signal being obtained by subtracting the output signal of the HPF unit from the output signal of the HPF unit. The estimation unit controls the cutoff frequency of a variable HPF unit that extracts a signal component for high-frequency interpolation from the harmonic signal on the basis of the estimated missing band.