CML - Digital Voice - CMX608/618/638

As a members of the CML DuraTALK family of digital voice products, the CMX608/CMX618/CMX638 are flexible, high integration, high performance, RALCWI Vocoders, offering near toll-quality voice at very low bit rates.

  • CMX608: Half-duplex RALCWI Vocoder
  • CMX618: Half-duplex RALCWI Vocoder with Integrated Voice Codec
  • CMX638: Full-duplex RALCWI Vocoder with Integrated Voice Codec

A Forward Error Correction (FEC) engine provides optimum performance in real life applications. The RALCWI Vocoder comprises four independent functions which are selectable by the host: Voice Encoder, FEC Encoder, Voice Decoder and FEC Decoder. The CMX608 and CMX618 are half-duplex Vocoders and the CMX638 is a full-duplex Vocoder with integrated voice CODEC. The CMX618 includes an integrated voice CODEC, offering a complete analogue voice to low bit rate vocoded data function, with integrated channel filters removing the need for external components, whereas the CMX608 requires an external voice CODEC.

The CMX608, CMX618 and CMX638 all operate from a dual power supply (1.8V and 3.3V) and are available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages. In encode mode, the voice encoder uses a 20ms voice frame size with 2 programmable bit rates:2400bps or 2750bps. The optional FEC encoder performs channel coding of the encoded voice ( 2400bps or 2750bps, depending on the selected mode) and forms an encoded, interleaved bit-stream of 3600bps (216 bits per 60ms packet or 288 bits per 80ms packet). The FEC operation utilises a packet of either 3 or 4 x 20ms Vocoder frames to provide optimum error correction performance.

In decode mode, the optional FEC decoder performs de-interleaving and channel decoding of the coded bit-stream (216 bits per 60ms packet or 288 bits per 80ms packet) and forms an error-corrected bit-stream of encoded voice at  2400bps or 2750bps rate, depending on the selected mode. The FEC decoder can optionally use "soft decision" metrics to improve its decoding ability. The voice decoder then converts the error-corrected bit-stream back into a digitised voice signal. Soft Decision Decoding (SDD), Discontinuous Transmission detection (DTX), Voice Activity Detection (VAD) and Comfort Noise Generation (CNG) functions are also included, to further enhance the overall performance.

Single (STD) and Dual (DTMF) Tones can be detected and sent separately in the coded bit-stream, then regenerated at the far end.

Function Add-ins
New features or enhancements to aid Vocoder operation. Function Add-ins currently available to these products are:

Voice Store and Retrieve (VSR)
Allows voice messages to be recorded and played back using on-chip memory. Eight phrase blocks, each capable of storing a minimum of five seconds of speech, are available from the CMX6x8.

Noise Gate
To remove background noise in between speech pauses.

To provide voice encryption sufficient to prevent casual eavesdropping.

Fine Analogue Output Gain Option
The fine analogue output gain option equips the vocoder device with improved output gain control.


  • RALCWI™ CML's Digital Voice Technology
  • Near Toll Quality RALCWI™ Coding Algorithm
  • No royalty/license fee
  • Multiple Bit-Rate Modes
    • 2400 or 2750 bps
    • 3600 bps with FEC Enabled
  • 4-bit Viterbi Soft Decision Decoding
  • Integrated Voice Codec(CMX618 and CMX638 only)
  • Integrated Input and Output Channel Filters
  • 20ms, 40ms, 60ms and 80ms Packet Lengths
  • No Licensing or Royalty Payments
  • Ancillary Audio Functions:
    • Voice Activity Detector
    • Comfort Noise Generator
    • DTMF and Single Tone Regeneration
  • Voice Store and Retrieve, Encryption and Noise Gate. Fine Analogue Output Gain. Function Add-ins Available
  • Voice Activity Detector, DTMF/Tone generator, comfort noise generator, soft decision decoding


  • Digital Trunking, Digital WLL
  • Digital-voice Scrambling and Encryption
  • Voice-storage and Playback Systems
  • Messaging Systems
  • VoIP Systems
  • Voice Pagers
  • Regenerative Digital Voice Repeaters

Supply Requirement:

  • 1.8V, 3.3V Tolerant I/O