Product category:
Communications ICs (Wired)
News Release from: CML Microcircuits | Subject: CMX638
Edited by the Electronicstalk Editorial
Team on 21 April 2008
Vocoders boost voice quality
Vocoder applications include voice storage and playback devices, VoIP, voice pagers, digital WLL, digital PMR/LMR, voice radio, digital trunking and regenerative digital voice repeaters.
CML Microcircuits' CMX638 is a flexible, highly integrated, high-performance duplex vocoder, using RALCWI (robust advanced low complexity waveform interpolation) technology CML now offers the CMX608, CMX618 and CMX638 high-performance vocoders, which all offer near toll-quality voice performance at very low bit-rates
This article was originally published on Electronicstalk on 11 Feb 2004 at 8.00am (UK)
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A forward error correction (FEC) engine provides optimum performance in real-life applications, with the RALCWI vocoder being comprised of four independent functions, which are selectable by the host: a voice encoder, FEC encoder, voice decoder, and FEC decoder.
The CMX608 and CMX618 are half-duplex ICs, with the new CMX638 offering full-duplex capability.
The CMX618 and CMX638 include an integrated voice CODEC, for complete analogue voice to low bit-rate vocoded data functions (with integrated channel filters, removing the need for external components).
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The CMX608 is offered without the CODEC, for customers wishing to use a different CODEC solution.
The voice encoder uses a 20ms voice frame size, with three programmable bit rates (2050, 2400 or 2750bps).
The optional FEC encoder performs channel coding of the encoded voice (at the rate selected) and forms an encoded, interleaved bit-stream of 3600bps (216 bits per 60ms packet or 288 bits per 80ms packet).
The FEC operation uses a packet of either 3 or 4 x 20ms vocoder frames for optimum error correction performance.
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 2050, 2400 or 2750bps, depending on the mode selected.
The FEC decoder can optionally use 'soft-decision' metrics to enhance its decoding ability.
The voice decoder then converts the error-corrected bit-stream back to a digitised voice signal.
The sytem supports soft decision decoding (SDD), Discontinuous transmission detection (DTX), voice activity detection (VAD) and comfort noise generation (CNG).
Single (STD) and dual (DTMF) tones can be detected, sent separately in the coded bit-stream, then regenerated at the far-end.
Vocoder applications include voice storage and playback devices, VoIP, voice pagers, digital WLL, digital PMR/LMR, voice radio, digital trunking, regenerative digital voice repeaters, digital voice scrambling and encryption.
All three products operate from dual power supply (1.8 and 3.3V) and are available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages.
Full vocoder product information is available on the CML website, with design support and applications consultation available from CML's global technical support teams.
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