EVRC

EVRC

Variable cellular telephony Speech Codec

Enhanced Variable Rate Coder

Background2a

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

Availability

Platforms
Texas Instruments – TI TMS320C6000 C64x / C64x+/ C66x / C674x

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

Specifications

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

Description

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

Applications

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

Voice over Packet (Gateways)

Streaming Media Servers

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