The audio codec is the cornerstone of modern digital telephony. It is the component that converts audible speech into digital data and back to audible speech again. In this application note, the A/D channels of the MAXQ3120 and an external DAC are used to encode and decode speech in standard µ-law and A-law format. This leaves a significant amount of processing horsepower available to perform other telecom-related functions, such as call-progress detection and generation, PCM framing, and silent-channel detection.