CML - Digital Voice - CMX7261

The CMX7261 Multi-transcoder IC is a member of the CML DuraTALK family of digital voice products providing multiple speech coders and an analogue audio codec in a single chip.

The CMX7261 features voice encoding and decoding through an Analogue Front End or transcoding operations over its digital interfaces. Both half-duplex and full-duplex modes are available. Input data and control are via an SPI compatible C-BUS which has a write-through ability to manage an external SPI controlled device using only one host SPI interface. C-BUS supports single SPI transactions or streaming modes via embedded hardware FIFOs. The CMX7261 utilises CML’s proprietary FirmASIC® component technology. On-chip sub-systems are configured by a Function Image data file that is uploaded during device initialisation and defining the device's function and feature set. The Function Image™ Host can be loaded by the host or auto-loaded from an external serial memory.

Two Function Images are currently available:


  • linear PCM, CVSD and G.729A speech coders
  • 8, 16 and 32 kHz sampling
  • Packed and unpacked frame formats
  • µ-law, A-law PCM compression
  • Voice Activity Detection


  • linear PCM and G.723.1 speech coders
  • G.723.1 at 5.3kbps and 6.3kbps
  • 8, 16 and 32 kHz sampling
  • µ-law, A-law compression
  • DTX function with Voice Activity Detection
  • Lost Packet Recovery

The device's functions and features can be enhanced by subsequent Function Image™ releases, simplifying in-the-field upgrades.

Block Diagram


  • No Audio Codec Required
  • No DSP  nor DSP Skills Required
  • Full and Half-duplex Operation
  • Encoding, Decoding and Transcoding
  • Mutiple Voice Coding Algorithms Supported
    • Linear PCM
    • G.711 ( µ-law, A-law)
    • G.729A
    • G.723.1
    • CVSD
  • Transcoder Routing:
    • Choice of Input Sources: C-BUS/Host, PCM Codec, Analogue Audio Inputs
    • Choice of Output Sources: C-BUS/Host, PCM Codec, Analogue Audio Outputs
    • Voice Activity Detection (VAD)
  • C-BUS Host Serial Data/Control Interface
    • SPI compatible with Register Mapping
    • Read/Write 128byte FIFOs
    • Streaming data transfer
  • Auxiliary GPIO Functions
  • Master/Slave PCM Serial Interface for External Audio Codec


  • Duplex and Half Duplex Digital Radio Systems
  • Personal Area Network Voice Links
  • Privacy-type Digital Voice Communications
  • Wireless PBX
  • Voice over IP (VoIP) Applications
  • Digital Software Defined Radio (SDR)

Supply Requirement:

  • 3.0 to 3.6 V