A full duplex ADPCM voice coder for use in the Ferranti Zonephone

A voice coder subsystem using the TMS320C10 DSP and a codec with an interfacing ASIC has been shown to be a practical realisation for CT2 (the second generation cordless telephone). The reduced G.721 ADPCM algorithm discussed is currently available as a standard ready-masked DSP device. Speech quality and signal to noise has been compared with that of a G.721 voice coder using typical speech signals. The results indicate a slight improvement of both parameters. Formal approval of the device for use in CT2 has been obtained. The design has met the requirements of this application. An upgraded version of the design, based on a custom-designed DSP, has been introduced recently for the new CAI standard. Whilst the latter version offers better power consumption and a higher degree of integration, the original DSP design was the first such speech coder system to have been designed and remains a practical and competitive design solution