COMMUNICATION APPARATUS FOR SPEECH SIGNAL

A speech signal communication apparatus used in a confidential communication system, which performs blockwise processing to achieve a high level of confidentiality, free from waveform discontinuity at the block boundary in a restored speech signal. This apparatus includes a calculating unit for calculating linear predictive coefficients of the input speech signal and a filter to inversely filter the speech signal by using the linear predictive coefficients. The filter flattens the spectral envelope of the input speech signal and produces a predictive residual signal therefrom. This apparatus also includes a removing unit for adaptively removing a low power frequency component from the frequency components of the predictive residual signal. The removing unit uses the linear predictive coefficients to determine which frequency components are to be removed. The linearly predictive coefficients are then converted into a signal having the removed frequency components therein. This converted signal is combined with the removed predictive residual signal from the removing unit, thereby producing a waveform continuous at block boundaries in a restored speech signal.