High efficiency speech coding apparatus and transit switching system employing the same

摘要

A high efficiency speech coding apparatus which can eliminate repetitions of high efficiency speech coding and decoding processes of a digital speech signal upon inter-office transit switching without employing a special exchange and a transit switching system which can prevent degradation in quality of speech information and increase in encode and decode processing delay upon transit switching are disclosed. The apparatus repetitively inserts a synchronizing signal into an output speech signal to an exchange and supervises an input speech signal from the exchange to detect a synchronizing signal in order to determine whether the destination of connection of the exchange is a subscriber line or another trunk circuit connected by way of another high efficiency coding apparatus. When a subscriber line is connected, code conversion and inverse code conversion between a high efficiency coded speech signal and a speech signal for the subscriber line are performed using a coding section and a decoding section, respectively. When another trunk circuit is connected, an invalid signal to raise the bit rate of the speech signal to allow transparent transmission through the exchange is added and removed bypassing the coding section and the decoding section.