Enhanced Variable Rate Speech Codec

Real-time implementation of the 3GPP2 standardized vocoder.

Features List

  • Functions are C-callable.
  • Multi–Channel Implementation.
  • Completely re–entrant (Channel can interrupt any Channel, any time)
  • The encoder and decoder meet all ITU EVRC compliance data files.
  • Includes Packet Loss Concealment Algorithm
  • Includes Support for Discontinuous Transmission (DTX)

Coding Rate: 8550, 4000, and 800 bits per second
Sampling Rate: 8 kHz
Delay: 20 milliseconds


Texas Instruments – TI TMS320C6000 C64x / C64x+/ C66x / C674x || TI TMS320C7000 C7x

ADT EVRC is available on the above Platforms: Other configurations are available upon request.


NOTE: We specify MIPS (Millions of Instructions Per Second) as MCPS (Millions of Instruction Cycles Per Second). Unless otherwise specified, peak MIPS are indicated.


The Adaptive Digital Technologies Enhanced Variable Rate Coder (EVRC) is a real-time implementation of the 3GPP2 standardized vocoder. The vocoder, originally developed for cellular telephony, also has other applications in VoIP.

EVRC compresses each 20 msec of 8000 Hz, 16-bit sampled speech input into output frames of one of three different sizes: full rate – 171 bits (8.55 kbit/s), half rate – 80 bits (4.0 kbit/s), eighth rate – 16 bits (0.8 kbit/s). A quarter rate was not originally included in the EVRC specification and eventually became part of EVRC-B.

Function APIs

API function call summary

EVRCENC_ADT_init      Initializes an Encode
ChannelEVRCDEC_ADT_init    Initializes an Decode Channel
EVRCENC_ADT_encode    Encodes a frame of data
EVRCDEC_ADT_decode    Decodes a frame of data


Wireless/Mobile/Personal Communications (base-stations and handset)

Voice over Packet (Gateways)

Streaming Media Servers

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