3 Definitions, symbols and abbreviations

06.423GPPTSVoice Activity Detection (VAD) for Half Rate Speech Traffic Channels

3.1 Definitions

For the purposes of the present document, the following terms and definitions apply:

mobile environment: any environment in which MSs may be used.

noise: signal component resulting from acoustic environmental noise.

3.2 Symbols

For the purposes of the present document, the following symbols apply:

3.2.1 Variables

aav1 filter predictor values, see clause 5.2.3

acf the ACF vector which is calculated in the speech encoder (GSM 06.20 [2])

adaptcount secondary hangover counter, see clause 5.2.6

av0 averaged ACF vector, see clause 5.2.2

av1 a previous value of av0, see clause 5.2.2

burstcount speech burst length counter, see clause 5.2.7

den denominator of left hand side of equation 8 in annex C, see clause 5.2.5

difference difference between consecutive values of dm, see clause 5.2.4

dm spectral distortion measure, see clause 5.2.4

hangcount primary hangover counter, see clause 5.2.7

lagcount number of subframes in current frame meeting periodicity criterion, see clause 5.2.9

lastdm previous value of dm, see clause 5.2.4

lags the open loop long term predictor lags for the four speech encoder subframes (GSM 06.20 [2].)

num numerator of left hand side of equation 8 in annex C, see clause 5.2.5

oldlagcount previous value of lagcount, see clause 5.2.9

prederr fourth order short term prediction error, see clause 5.2.5

ptch Boolean flag indicating the presence of a periodic signal component, see clause 5.2.9

pvad energy in the current filtered signal frame, see clause 5.2.1

rav1 autocorrelation vector obtained from av1, see clause 5.2.3

rc the first four unquantized reflection coefficients calculated in the speech encoder (GSM 06.20 [2])

rvad autocorrelation vector of the adaptive filter predictor values, see clause 5.2.6

smallag difference between consecutive lag values, see clause 5.2.9

stat Boolean flag indicating that the frequency spectrum of the input signal is stationary, see clause 5.2.4

thvad adaptive primary VAD threshold, see clause 5.2.6

tone Boolean flag indicating the presence of an information tone, see clause 5.2.5

vadflag Boolean VAD decision with hangover included, see clause 5.2.8

veryoldlagcount previous value of oldlagcount, see clause 5.2.9

vvad Boolean VAD decision before hangover, see clause 5.2.7

3.2.2 Constants

adp number of frames of hangover for secondary VAD, see clause 5.2.6

burstconst minimum length of speech burst to which hangover is added, see clause 5.2.8

dec determines rate of decrease in adaptive threshold, see clause 5.2.6

fac determines steady state adaptive threshold, see clause 5.2.6

frames number of frames over which av0 and av1 are calculated, see clause 5.2.2

freqth threshold for pole frequency decision, see clause 5.2.5

hangconst number of frames of hangover for primary VAD, see clause 5.2.8

inc determines rate of increase in adaptive threshold, see clause 5.2.6

lthresh lag difference threshold for periodicity decision, see clause 5.2.9

margin determines upper limit for adaptive threshold, see clause 5.2.6

nthresh frame count threshold for periodicity decision, see clause 5.2.9

plev lower limit for adaptive threshold, see clause 5.2.6

predth threshold for short term prediction error, see clause 5.2.5

pth energy threshold, see clause 5.2.6

thresh decision threshold for evaluation of stat flag, clause 5.2.4

3.2.3 Functions

+ addition

‑ subtraction

* multiplication

/ division

| x | absolute value of x

AND Boolean AND

OR Boolean OR

b

MULT(x(i)) the product of the series x(i) for i=a to b

i=a

b

SUM(x(i)) the sum of the series x(i) for i=a to b

i=a

3.3 Abbreviations

For the purposes of the present document, the following abbreviations apply:

ACF Autocorrelation Function

AFLAT Autocorrelation Fixed point LAttice Technique

ANSI American National Standards Institute

DTX Discontinuous Transmission

LTP Long Term Predictor

TX Transmission

VAD Voice Activity Detector

For abbreviations not given in this clause see GSM 01.04 [1].