RALCWI Vocoder
CMX608/CMX618/CMX638
In encode mode, the voice encoder uses a 20ms voice frame size with two 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.
New features and enhancements to existing functions may be provided from time to time, expanding the
capabilities of the Vocoder. These are provided as Function Images™, a hex format file that can be loaded
via the C-BUS at run-time. Function Images™ can be downloaded from the CML Portal, a secure area of
the CML website. Details of currently available Function Images™ can be found in the
CMX608/CMX618/CMX638 Product page on the CML website.
2014 CML Microsystems Plc
2
D/608_18_38/11
CMLMICRO [ CML MICROCIRCUITS ]
