Design of a full-featured, solid-state telephone answering device

The authors discuss the use of advanced digital signal processing (DSP) algorithms to implement sophisticated audio processing functions and microcontroller tasks on a low-cost digital signal processor, enabling OEM (original equipment manufacturer) vendors to build cost-effective solid-state telephone answering devices. Sophisticated data compression algorithms and a low-cost programmable DSP processor were used to develop a powerful set of telephone-answering-machine chips. The DSP-based chip sets have been integrated in devices that offer incoming message recording times from 5 to 25 min, outgoing messages, time/date voice stamping and many other advanced features. A key to the project was finding application areas where DSP software could replace the traditional hardware while providing higher performance at lower cost. Speech processing along with telephony provided that environment. Aspects of hardware and software design are discussed