3 Definitions, abbreviations and mathematical expressions

26.4453GPPCodec for Enhanced Voice Services (EVS)Detailed algorithmic descriptionRelease 15TS

3.1 Definitions

For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].

frame: an array of audio samples spanning 20ms time duration.

EVS codec: The EVS codec includes two operational modes: EVS Primary operational mode (EVS Primary mode) and EVS AMR-WB Inter-Operable modes (EVS AMR-WB IO mode). When using the EVS AMR-WB IO mode the speech frames are bitstream interoperable with the AMR-WB codec [9]. Frames generated by an EVS AMR-WB IO mode encoder can be decoded by an AMR-WB decoder, without the need for transcoding. Likewise, frames generated by an AMR-WB encoder can be decoded by an EVS AMR-WB IO mode decoder, without the need for transcoding.

EVS Primary mode: Includes 11 bit-rates for fixed-rate or multi-rate operation; 1 average bit-rate for variable bit-rate operation; and 1 bit-rate for SID (3GPP TS 26.441 [2]). The EVS Primary mode can encode narrowband, wideband, super-wideband and fullband signals. None of these bit-rates are interoperable with the AMR-WB codec.

EVS AMR-WB IO mode: Includes 9 codec modes and SID. All are bitstream interoperable with the AMR-WB codec (3GPP TS 26.171 ‎[37‎]).

Operational mode: Used for the EVS codec to distinguish between EVS Primary mode and EVS AMR-WB IO mode.

3.2 Abbreviations

For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].

ACELP Algebraic Code-Excited Linear Prediction

AMR Adaptive Multi Rate (codec)

AMR-NB Adaptive Multi Rate Narrowband (codec) – Also referred to as AMR

AMR-WB Adaptive Multi Rate Wideband (codec)

AR Auto-Regressive

AVQ Algebraic Vector Quantization

CELP Code-Excited Linear Prediction

CLDFB Complex Low Delay Filter Bank

CMR Codec Mode Request

CNG Comfort Noise Generator

DCT Discrete Cosine Transformation

DFT Discrete Fourier Transform

DTX Discontinuous Transmission

EFR Enhanced Full Rate (codec)

EVS Enhanced Voice Services

FB Fullband

FCB Fixed Codebook

FEC Frame Erasure Concealment

FFT Fast Fourier Transform

FIR Finite Impulse Response

FT Frame Type

GC Generic Coding

HF High Frequency

HP High Pass

IIR Infinite Impulse Response

IP Internet Protocol

ISF Immittance Spectral Frequency

ISP Immittance Spectral Pair

ISPP Interleaved Single-Pulse Permutation

JBM Jitter Buffer Management

LD Low Delay

LP Linear Prediction

LPF Low Pass Filter

LSB Least Significant Bit

LSF Line Spectral Frequency

LSP Line Spectral Pair

LTP Long-Term Prediction

MA Moving Average

MDCT Modified Discrete Cosine Transform

MRLVQ Multi-Rate Lattice Vector Quantization

MSB Most Significant Bit

MSVQ Multi-Stage Vector Quantization

MTSI Multimedia Telephony Service for IMS

NB Narrowband

OL Open-Loop

PCPRS Path-Choose Pulse Replacement Search

PS Packet Switched

PSTN Public Switched Telephone Network

QMF Quadrature Mirror Filter (See also CLDFB)

SAD Signal Activity Detection

SDP Session Description Protocol

SID Silence Insertion Descriptor

SNR Signal-to-Noise Ratio

SWB Super Wideband

TC Transition Coding

ToC Table of Contents

UC Unvoiced Coding

VC Voiced Coding

VMR-WB Variable Rate Multimode Wideband

VQ Vector Quantization

WB Wideband

WMOPS Weighted Millions of Operations Per Second

3.3 Mathematical Expressions

For the purposes of the present document, the following conventions apply to mathematical expressions:

indicates the largest integer less than or equal to x: , and ;

indicates the smallest integer greater than or equal to x: , and

|x| indicates the absolute value of x: |17| = 17, |–17| = 17;

min(x0,…xN–1) indicates the minimum of x0,…, xN–1, N being the number of components;

max(x0,…xN–1) indicates the maximum of x0, …, xN–1;

AT indicates the transpose of matrix A;

indicates the remainder after dividing x by y: ;

round(x) is traditional rounding: round(x) = ;

exp(x) is equivalent to ex where e is the base of the natural algorithm;

indicates summation;

indicates product;

Unless otherwise specified, log(x) denotes logarithm at base 10 throughout this Recommendation.