A decoding
processing portion 11 of a speech decoder 10 is provided with an emphasis
processing portion 15 for performing an emphasis process on signals to be processed (excited signals) SPC generated from coded speech signals BS. A counter portion 17 counts the number of times code errors occurred in successive frames of the coded speech
signal BS, and outputs the successive frame error number. When the successive frame error number outputted form the counter portion 17 is less than or equal to a preset reference successive frame error number, a first switch SW1 and second switch SW2 are set to an emphasis
processing portion 15 side. Accordingly, the signals to be processed SPC generated from various parameters included in the coded speech signals are supplied through the switch SW1 to the emphasis processing portion 15 of the decoding processing portion 11 to perform an emphasis process. Then, the emphasized signals to be processed SEPC obtained by this emphasis process are outputted through the switch SW2 to latter connected devices. As a result, decoded speech signals SP with good subjective
sound quality are obtained. On the other hand, when the
communication quality is degraded and the successive frame error number outputted from the counter portion 17 exceeds a preset reference successive frame error number, the first switch SW1 and second switch SW2 are set to a bypass BP side. Accordingly, the signals to be processed SPC generated from the various parameters contained in the coded speech signals are outputted to the latter connected devices without emphasis processing by the emphasis processing portion 15. In this way, emphasis processing is prohibited when the successive frame error number is large, thereby reducing
distortion generated in the decoded speech signals SP.