EVRC

Speech Codec

Enhanced Variable Rate Coder

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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.

EVRC C6xx

CPU Utilization & Memory Requirements
All Memory usage is given in units of byte.
SoftwareMIPS – Peak LoadingProgram MemoryData MemoryScratchPer Channel Data Memory
EVRC125175k15k5k6k

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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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