Description of a hybrid 7.2 kbps vocoder

A speech bandwidth compression system is described which employs a hybrid processing approach combining a baseband system and a Linear Predictive Coding system to produce high quality speech at a transmission rate of 7.2 Kbps. The system requires the extraction and transmission of excitation parameters, but is not very sensitive to errors in those parameters nor is it particularly sensitive to errors in the baseband portion of the processing. Since the system is composed of two independent processes, errors in one process have no effect on the other process and the system is remarkably robust. The system is essentially a modification of a similar system which was operated at 16 Kbps (1) which utilizes unique coding techniques to reduce the bit rate to 7.2 Kbps.