EVRC Speech Codec B


EVRC ADAPTIVE DIGITAL'S ENHANCED VARIABLE RATE CODEC B

EVRC - B  SPEECH CODER    C64x,    C55x

DESCRIPTION

Enhanced Variable Rate Codec B (EVRC-B) is a speech codec used by CDMA (Code Division Multiple Access) networks. EVRC-B is an extension to EVRC and compresses each 20 millisecond FRAMES of 8000 Hz, 16-bit sampled speech input into output frames of one of the four different sizes: Rate 1 - 171 bits/frame, Rate 1/2 - 80 bits/frame, Rate 1/4 - 40 bits/frame, Rate 1/8 - 16 bits/frame.

One significant enhancement in EVRC-B is the use of 1/4-rate frames that were not used in EVRC. The EVRC-B makes use of the intermediate coding rates through increased awareness of the nature of the individual speech samples. This provides lower average data rates compared to EVRC, for a given voice quality.

The EVRC-B codec is a multimode codec. It supports full rate, half rate, quarter rate and eighth rate narrow band speech encoding/decoding modes.  The decoder performs eighth rate (noise), quarter rate NELP,  half rate CELP, full rate CELP and half and full rate PPP.

The EVRC-B decoder works on various rate packets, performs FEC and generates 20msec speech data frames. With a sampling frequency of 8000Hz the decoder output frame contains 160 input samples. The format of the output samples is assumed to be 16 bit uniformly quantized (linear). 

Data sheet:C64x .pdf

Data sheet:C55x - xdm .pdf

Coding Rate:8.5, 4.0, 2.0, and 0.8 kbps

Sampling Rate: 8 kHz

Delay: 20 milliseconds

EVRC FEATURES

  1. Functions are C-callable.
  2. Multi–Channel capable.
  3. Can be integrated with echo cancellers, and tone detection/regeneration.
  4. Encodes frames of 20 ms sampled at 8KHz (160 samples) using above algorithms.
  5. Bit-exact with all EVRCB 3GPP2 test sequences
  6. The implementation support run time table relocation
  7. Fully interruptible Code
  8. Efficient scratch memory management with reduced stack requirements
  9. The C55x implementation is xDAIS/xDM1.0 complaint.

AVAILABILITY

ADT EVRC is available on the TMS320C6000™ DSP, & C5000™ DSP Families

C64x™DSP, C55x™DSPGenerations


SPECIFICATIONS

EVRC- B C64xx

All memory requirements are in units of byte.

Software MIPS Program Memory Data Memory Scratch Per-Channel Data Memory
Average Max
Encode 50.2 83.5 263.5k 0.7k 3008 7240
Decode 11.1 27.1 2176

 

EVRC- B C55x - XDM - Cycles Information

Configuration ID Performance Statistics (IN MEGACYCLES /SEC) 1
Average Peak
EVRCB encode NA 23.10
EVRCB decode NA 8.10
EVRCB full duplex NA 31.20


Measured with all program, constant tables, instance and CDP in SARAM, scratch in DARAM. All performance statistics with   DTMF and TTY flags turned off.

Memory Statistics C55x - XDM

Configuration Memory Statistics2
Program
MEMORY		 Data Memory Total
Internal External Stack
SP SSP
EVRCB encode 83.94 45.81 0 0.51 0.51 130.77
EVRCB decode 53.09 44.46 0 0.4 0.4 98.35
EVRCB full duplex 118.7 48.19 0 0.51 0.51 167.91

2 All memory requirements are expressed in kilobytes (1 kilobyte = 1024 8-bit bytes).

 

FUNCTIONS


APPLICATIONS

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

 

 

 

 

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