SIST EN 300 973 V7.0.1:2003

Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Voice Activity Detector (VAD) for half rate speech traffic channels (GSM 06.42 version 7.0.1 Release 1998)

Upgrade from Phase 2+ to Release 1998

Digitalni celični telekomunikacijski sistem (faza 2+) – Govor s polovično hitrostjo – Detektor govornih dejavnosti (VAD) pri prometnih kanalih s polovično hitrostjo govora (GSM 06.42, različica 7.0.1, izdaja 1998)

General Information

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Mandate: T-172
• Ref Project: ETSI EN 300 973 V7.0.1 (2000-01) - Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Voice Activity Detector (VAD) for half rate speech traffic channels (GSM 06.42 version 7.0.1 Release 1998)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 300 973 V7.0.1:2003
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±*RYRUVSRORYLþQRKLWURVWMR±
'HWHNWRUJRYRUQLKGHMDYQRVWL9$'SULSURPHWQLKNDQDOLKVSRORYLþQRKLWURVWMR
JRYRUD*60UD]OLþLFDL]GDMD
Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Voice
Activity Detector (VAD) for half rate speech traffic channels (GSM 06.42 version 7.0.1
Release 1998)
Ta slovenski standard je istoveten z: EN 300 973 Version 7.0.1
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST EN 300 973 V7.0.1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 300 973 V7.0.1:2003

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SIST EN 300 973 V7.0.1:2003
ETSI EN 300 973 V7.0.1 (2000-01)
European Standard (Telecommunications series)
Digital cellular telecommunications system (Phase 2+);
Half rate speech;
Voice Activity Detector (VAD)
for half rate speech traffic channels
(GSM 06.42 version 7.0.1 Release 1998)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 2 ETSI EN 300 973 V7.0.1 (2000-01)
Reference
REN/SMG-110642Q7
Keywords
Digital cellular telecommunications system,
Global System for Mobile communications (GSM)
ETSI
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comment to: [e-mail]
Important notice
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In case of dispute, the reference shall be the printing on ETSI printers of the PDF version kept on a specific network
drive within ETSI Secretariat.
Copyright Notification
No part may be reproduced except as authorized by written permission.
The copyright and the foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 2000.
All rights reserved.
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 3 ETSI EN 300 973 V7.0.1 (2000-01)
Contents
Intellectual Property Rights.4
Foreword.4
1 Scope .6
2 References.6
3 Definitions, symbols and abbreviations .6
3.1 Definitions.6
3.2 Symbols.7
3.2.1 Variables.7
3.2.2 Constants.7
3.2.3 Functions.7
3.3 Abbreviations .8
4 General .8
5 Functional description.8
5.1 Overview and principles of operation.9
5.2 Algorithm description.9
5.2.1 Adaptive filtering and energy computation.10
5.2.2 ACF averaging.11
5.2.3 Predictor values computation.11
5.2.4 Spectral comparison.12
5.2.5 Information tone detection.12
5.2.6 Threshold adaptation .13
5.2.7 VAD decision .15
5.2.8 VAD hangover addition.15
5.2.9 Periodicity detection .15
6 Computational description overview .16
6.1 VAD modules.16
6.2 Pseudo-floating point arithmetic.16
Annex A (informative): VAD performance.18
Annex B (informative): Simplified block filtering operation.19
Annex C (informative): Pole frequency calculation.20
Annex D (informative): Change Request History .21
History .22
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 4 ETSI EN 300 973 V7.0.1 (2000-01)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect
of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server
(http://www.etsi.org/ipr).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in SR 000 314 (or the updates on the ETSI Web server)
which are, or may be, or may become, essential to the present document.
Foreword
This European Standard (Telecommunications series) has been produced by the Special Mobile Group (SMG).
The present document specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission
(DTX) within the digital cellular telecommunications system. The present document is part of a series covering the half
rate speech traffic channels as described below:
GSM 06.02 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Half rate speech
processing functions".
GSM 06.06 "Digital cellular telecommunications system (Phase 2+); Half rate speech; ANSI-C code for the
GSM half rate speech codec".
GSM 06.07 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Test sequences for the
GSM half rate speech codec".
GSM 06.20 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Half rate speech
transcoding".
GSM 06.21 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Substitution and muting
of lost frames for half rate speech traffic channels".
GSM 06.22 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Comfort noise aspects
for half rate speech traffic channels".
GSM 06.41 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Discontinuous
Transmission (DTX) for half rate speech traffic channels".
GSM 06.42 "Digital cellular telecommunications system (Phase 2+); Half rate speech; Voice Activity
Detector (VAD) for half rate speech traffic channels".
The contents of the present document is subject to continuing work within SMG and may change following formal SMG
approval. Should SMG modify the contents of the present document it will be re-released with an identifying change of
release date and an increase in version number as follows:
Version 7.x.y
where:
7 indicates Release 1998 of GSM Phase 2+.
x the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates,
etc.
y the third digit is incremented when editorial only changes have been incorporated in the specification.
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 5 ETSI EN 300 973 V7.0.1 (2000-01)
National transposition dates
Date of adoption of this EN: 31 December 1999
Date of latest announcement of this EN (doa): 31 March 2000
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 30 September 2000
Date of withdrawal of any conflicting National Standard (dow): 30 September 2000
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 6 ETSI EN 300 973 V7.0.1 (2000-01)
1 Scope
The present document specifies the Voice Activity Detector (VAD) to be used in the Discontinuous Transmission
(DTX) as described in GSM 06.41 [4]. It also specifies the test methods to be used to verify that a VAD implementation
complies with the present document.
The requirements are mandatory on any VAD to be used either in GSM Mobile Stations (MS)s or Base Station Systems
(BSS)s that utilize the half-rate GSM speech traffic channel.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
• A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same
number.
• For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y).
[1] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and
acronyms".
[2] GSM 06.20: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Half rate
speech transcoding".
[3] GSM 06.22: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Comfort
noise aspects for half rate speech traffic channels".
[4] GSM 06.41: "Digital cellular telecommunications system (Phase 2+); Half rate speech;
Discontinuous Transmission (DTX) for half rate speech traffic channels".
[5] GSM 06.06: "Digital cellular telecommunications system (Phase 2+); Half rate speech; ANSI C
code for the GSM half rate speech codec".
[6] GSM 06.07: "Digital cellular telecommunications system (Phase 2+); Half rate speech; Test
sequences for the GSM half rate speech codec".
3 Definitions, symbols and abbreviations
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: The signal component resulting from acoustic environmental noise.
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 7 ETSI EN 300 973 V7.0.1 (2000-01)
3.2 Symbols
For the purposes of the present document, the following symbols apply:
3.2.1 Variables
aav1 filter predictor values, see subclause 5.2.3
acf the ACF vector which is calculated in the speech encoder (GSM 06.20 [2])
adaptcount secondary hangover counter, see subclause 5.2.6
av0 averaged ACF vector, see subclause 5.2.2
av1 a previous value of av0, see subclause 5.2.2
burstcount speech burst length counter, see subclause 5.2.7
den denominator of left hand side of equation 8 in annex C, see subclause 5.2.5
difference difference between consecutive values of dm, see subclause 5.2.4
dm spectral distortion measure, see subclause 5.2.4
hangcount primary hangover counter, see subclause 5.2.7
lagcount number of subframes in current frame meeting periodicity criterion, see subclause 5.2.9
lastdm previous value of dm, see subclause 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 subclause 5.2.5
oldlagcount previous value of lagcount, see subclause 5.2.9
prederr fourth order short term prediction error, see subclause 5.2.5
ptch Boolean flag indicating the presence of a periodic signal component, see subclause 5.2.9
pvad energy in the current filtered signal frame, see subclause 5.2.1
rav1 autocorrelation vector obtained from av1, see subclause 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 subclause 5.2.6
smallag difference between consecutive lag values, see subclause 5.2.9
stat Boolean flag indicating that the frequency spectrum of the input signal is stationary, see subclause
5.2.4
thvad adaptive primary VAD threshold, see subclause 5.2.6
tone Boolean flag indicating the presence of an information tone, see subclause 5.2.5
vadflag Boolean VAD decision with hangover included, see subclause 5.2.8
veryoldlagcount previous value of oldlagcount, see subclause 5.2.9
vvad Boolean VAD decision before hangover, see subclause 5.2.7
3.2.2 Constants
adp number of frames of hangover for secondary VAD, see subclause 5.2.6
burstconst minimum length of speech burst to which hangover is added, see subclause 5.2.8
dec determines rate of decrease in adaptive threshold, see subclause 5.2.6
fac determines steady state adaptive threshold, see subclause 5.2.6
frames number of frames over which av0 and av1 are calculated, see subclause 5.2.2
freqth threshold for pole frequency decision, see subclause 5.2.5
hangconst number of frames of hangover for primary VAD, see subclause 5.2.8
inc determines rate of increase in adaptive threshold, see subclause 5.2.6
lthresh lag difference threshold for periodicity decision, see subclause 5.2.9
margin determines upper limit for adaptive threshold, see subclause 5.2.6
nthresh frame count threshold for periodicity decision, see subclause 5.2.9
plev lower limit for adaptive threshold, see subclause 5.2.6
predth threshold for short term prediction error, see subclause 5.2.5
pth energy threshold, see subclause 5.2.6
thresh decision threshold for evaluation of stat flag, subclause 5.2.4
3.2.3 Functions
+ addition
- subtraction
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 8 ETSI EN 300 973 V7.0.1 (2000-01)
* 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 subclause see GSM 01.04 [1].
4 General
The function of the VAD is to indicate whether each 20 ms frame produced by the speech encoder contains speech or
not. The output is a Boolean flag (vadflag) which is used by the Transmit (TX) DTX handler defined in GSM 06.41 [4].
The present document is organized as follows:
Clause 5 describes the principles of operation of the VAD. Clause 6 provides an overview of the computational
description of the VAD. The computational details necessary for the fixed point implementation of the VAD algorithm
are given in the form of an American National Standards Institute (ANSI) C program contained in GSM 06.06 [5].
The verification of the VAD is based on the use of digital test sequences which are described in GSM 06.07 [6].
The performance of the VAD algorithm is characterized by the amount of audible speech clipping it introduces and the
percentage activity it indicates. The characteristics for the VAD defined in the present document have been established
by extensive testing under a wide range of operating conditions. The results are summarized in annex A.
5 Functional description
The purpose of this clause is to give the reader an understanding of the principles of operation of the VAD, whereas
GSM 06.06 [5] contains the fixed point computational description of the VAD. In the case of discrepancy between the
two descriptions, the description in GSM 06.06 [5] will prevail.
ETSI

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SIST EN 300 973 V7.0.1:2003
(GSM 06.42 version 7.0.1 Release 1998) 9 ETSI EN 300 973 V7.0.1 (2000-01)
5.1 Overview and principles of operation
The function of the VAD is to distinguish between noise with speech present and noise without speech present. This is
achieved by comparing the energy of a filtered version of the input signal with a threshold. The presence of speech is
indicated whenever the threshold is exceeded.
The detection of speech in mobile environments is difficult due to the low speech/noise ratios which are encountered,
particularly in moving vehicles. To increase the probability of detecting speech, the input signal is adaptively filtered
(see subclause 5.2.1) to reduce its noise content before the voice activity decision is made (see subclause 5.2.7).
The frequency spectrum and level of the noise may vary within a given environment as well as between different
environments. It is therefore necessary to adapt the input filter coefficients and energy threshold at regular intervals as
described in subclause 5.2.6.
5.2 Algorithm description
The block diagram of the VAD algorithm is shown in figure 1. The individual blocks are described in the following
subclauses. The gl
...