CML - Digital Voice - CMX649

As a member of the CML DuraTALK family of digital voice products, the CMX649 Adaptive Delta Modulation (ADM) Voice Codec provides full duplex codec functions optimised for cost effective, portable, wireless applications.

Standard and lower cost digital voice applications are supported via selectable operating modes. Robust ADM coding (eg. Continuously Variable Slope Delta modulation (CVSD)) simplifies protocol and host software design by eliminating the forward error correction and framing protocols required by other codec algorithms. Multiple codec sample/data rates are supported. Integrated filters reduce external components and adjust to match the selected codec sample rate. The use of both external and internal codec sample clock sources is supported.

Independent encoder and decoder powersave controls minimise power for half duplex wireless links. Baseband interfaces to microphone, loudspeaker, host µC and RF transceiver circuits do not require external transcoders or complex voice frame transfer protocols.

CMX649 Sound Samples

The CMX649 ADM Voice Codec IC provides full-duplex ADM, companded and linear PCM and transcoder functions for digital wireless communications. This demonstration provides a comparative ADM audio presentation of a range of CMX649 end-to-end (encode/decode) audio outputs using sampling rates of 16kb/s, 24kb/s, 32kb/s, 64kb/s and 128kb/s.

Use the links below to compare; for this demonstration you will need a good-quality sound system on your PC; with the volume set at a comfortable level. 

Audio Output at 16kb/s
Audio Output at 24kb/s
Audio Output at 32kb/s
Audio Output at 64kb/s
Audio Output at 128kb/s


  • CVSD for Digital Voice Communication
  • Adaptive Delta Modulation (ADM)
  • Non Linear PCM: µ-Law and A-Law Modes
  • 13-Bit Linear PCM Codec
  • Programmable Analogue Inputs and Outputs, Time Constants for ADM Codec andAnti-Alias and Anti-Image filters
  • Clock and Data Recovery
  • Wide Data-Rate Range: 16 to 128 kb/s
  • Programmable Voice Activity Detector (VAD)
  • Transcoding, internal/external sample clocking and flexible uC interfaces


  • Digital Cordless Headsets and Telephones
  • Personal Area Network (PAN) Voice Links
  • Wireless Digital PBX
  • Full-Duplex Digital Radio Systems
  • Time-Division Duplex (TDD) Systems
  • Portable Digital Voice Communicators
  • Voice Storage and Voice Delay

Supply Requirement:

  • 2.7 to 5.5 V