The AD1843 SoundComm™ Codec is a complete analog front end for high performance DSP-based telephony and audio applications. The device integrates the real-world analog I/O requirements for many popular functions thereby reducing size, power consumption, and system complexity. The AD1843 SoundComm is the world's first codec which can support four different sample rates simultaneously, without any beat frequency noise issues. This is essential for highly integrated audio/ modem/fax products since the sample rates associated with audio are very much distinct from the sample rates associated with telephony-oriented data communication. It is also the first codec to offer on-chip digital phase lock loops for sample rate synchronization to external clock signals. This sample rate flexibility is enabled through Analog Devices' Continuous Time Oversampling (CTO) technology.

The main elements of the AD1843 are its extensive input and mixing section, its two channels of sigma-delta analog-to-digital conversion, its four channels of sigma delta digital-to-analog conversion, its digital filters, and the clock and control circuitry for implementing the device's different modes. The AD1843 permits flexible sample-rate selection through programming and external synchronization, many input and output options, and many mixing options.

The versatility of the device is shown by the following examples of functions it can perform:

• Stereo audio input and/or quad output, simultaneously at different sample rates.
• Stereo audio output with simultaneous full duplex modem or fax operation with frequency and phase resampling.
• Mono audio input and stero audio output with simultaneous modem receive and transmit for simultaneous voice and data communications.
• Dual independent audio inputs with audio output for echo cancelling speakerphones.