SIST EN 300 973 V7.0.1:2003
(Main)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)
- Abstract
Upgrade from Phase 2+ to Release 1998
- Status
- Published
- Publication Date
- 30-Nov-2003
- 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
SIST EN 300 973 V7.0.1:2003 is the Slovenian adoption of ETSI EN 300 973 Version 7.0.1. It specifies the Voice Activity Detector (VAD) used in Digital cellular telecommunications system (Phase 2+) (GSM) half rate speech traffic channels, and the test methods used to verify VAD implementations. The document is intended for GSM Mobile Stations (MS) and Base Station Systems (BSS) that use Discontinuous Transmission (DTX).
What does SIST EN 300 973 V7.0.1:2003 specify?
SIST EN 300 973 V7.0.1:2003 specifies how a VAD decides whether each 20 ms speech frame contains speech or only background noise, and it defines the verification methods for that decision. The standard is mandatory for VADs used in GSM MS and BSS that operate on the half-rate speech traffic channel.
The document is organized into:
- Clause 1: scope
- Clause 2: references
- Clause 3: definitions, symbols and abbreviations
- Clause 4: general
- Clause 5: functional description
- Clause 6: computational description overview
- Annexes A-D: informative material
| Annex | What it covers |
|---|---|
| Annex A | VAD performance |
| Annex B | Simplified block filtering operation |
| Annex C | Pole frequency calculation |
| Annex D | Change Request History |
What are the key requirements of SIST EN 300 973 V7.0.1:2003?
The core requirement in SIST EN 300 973 V7.0.1:2003 is that the VAD shall produce a Boolean output, vadflag, indicating speech activity for each 20 ms frame, and that output is used by the TX DTX handler defined in GSM 06.41. In practice, this is the speech/no-speech decision that controls whether transmission continues or enters DTX.
Frame-by-frame VAD decision
Clause 5.2.7 defines the preliminary decision vvad as a comparison between the filtered frame energy pvad and the adaptive threshold thvad. This means implementers must compute the same energy and threshold values, because the decision is entirely based on that comparison.
Adaptive filtering and energy computation
Clause 5.2.1 computes pvad from the filtered signal and the autocorrelation values acf. The purpose is to estimate energy after adaptive filtering, so the VAD is less sensitive to noise than a simple raw-energy check. In practice, this is the quantity that is compared with the adaptive threshold.
ACF averaging and predictor values
Clause 5.2.2 averages acf vectors over 4 frames, and clause 5.2.3 derives predictor values from av1 before forming rav1. This gives the VAD a longer view of the signal spectrum than one frame alone. For implementation, it means the algorithm keeps frame history and uses it to stabilize later decisions.
Spectral comparison and stationary-signal detection
Clause 5.2.4 compares rav1 and av0 using the distortion measure dm, then sets the Boolean stat from the change in dm. This tells the VAD whether the spectrum is stationary. In practice, stat is part of the condition that allows threshold adaptation, so the VAD only adapts when the signal looks stable enough.
Information tone detection
Clause 5.2.5 detects tones by testing short term prediction error and pole frequency. It uses predth and freqth to reject tones and low-frequency resonances such as some vehicle noise. This matters because tones can look like speech to simpler detectors, so the VAD needs a separate tone test to avoid false activity decisions.
Threshold adaptation
Clause 5.2.6 updates thvad every 20 ms when the signal conditions allow it. The threshold is lowered or raised with controlled rates, limited by plev, fac, inc, dec, margin, pth and adp. In practice, this keeps the detector responsive across different noise levels without letting the threshold drift too far.
Hangover and periodicity control
Clause 5.2.8 adds hangover only after speech bursts reach burstconst, and clause 5.2.9 uses periodicity detection from LTP lag values to protect vowel-like sounds from unwanted adaptation. This is important because short speech pauses and periodic voiced sounds can otherwise be clipped. The output vadflag therefore includes both the direct speech decision and a short hold time that preserves natural speech.
What terms does SIST EN 300 973 V7.0.1:2003 define?
- mobile environment - Any environment in which MSs may be used.
- noise - The signal component resulting from acoustic environmental noise.
- ACF (Autocorrelation Function) - A function used in the speech encoder and in the VAD to represent signal correlation across samples.
- DTX (Discontinuous Transmission) - The transmission mode that suppresses sending during non-speech periods.
- LTP (Long Term Predictor) - The predictor in the speech codec whose lag values are used by the periodicity detector.
- TX (Transmit) - The transmission side that uses the
vadflagoutput in the DTX handler. - VAD (Voice Activity Detector) - The function that decides whether each frame contains speech.
Who uses SIST EN 300 973 V7.0.1:2003?
SIST EN 300 973 V7.0.1:2003 is used by GSM speech codec designers, radio and baseband engineers, and implementers of DTX in MS and BSS equipment. It is also used by verification teams and test laboratories that need to check whether a VAD behaves as specified. Quality and product engineers use it to compare implementations against the same frame-based decision, threshold adaptation, and test-sequence behavior.
What changed in SIST EN 300 973 V7.0.1:2003 from the previous edition?
SIST EN 300 973 V7.0.1:2003 corresponds to the Release 1998 version of GSM 06.42, identified as version 7.0.1. Annex D records the version update to 7.0.1 for publication, and the foreword states that changes of substance and editorial changes are tracked through the version digits.
Which standards are used with SIST EN 300 973 V7.0.1:2003?
- GSM 01.04 - Supplies abbreviations and acronyms used when a term is not defined in this document.
- GSM 06.20 - Provides the half rate speech transcoding functions and the encoder data such as
acf,rcandlagsused by the VAD. - GSM 06.22 - Covers comfort noise aspects for half rate speech traffic channels.
- GSM 06.41 - Defines DTX for half rate speech traffic channels and the TX DTX handler that uses
vadflag. - GSM 06.06 - Contains the ANSI C code for the GSM half rate speech codec, including the fixed-point computational description.
- GSM 06.07 - Provides the test sequences used to verify VAD compliance.
For this Release 1998 document, references to GSM documents apply to the Release 1998 versions.
What does the SIST EN 300 973 V7.0.1:2003 document contain?
The document contains the functional block diagram of the VAD, the flow chart for threshold adaptation, and tables of constants and initial values used by the algorithm. It also gives the equations for adaptive filtering, ACF averaging, spectral comparison, tone detection, hangover addition, and periodicity detection. The computational overview explains how the VAD is split into ANSI C modules and how pseudo-floating point arithmetic is used for fixed-point implementation.
Annex A summarizes observed VAD performance in terms of speech clipping and channel activity. Annex B derives the simplified block filtering operation, and Annex C derives the pole-frequency test used in tone detection. Annex D records the change request history.
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Frequently Asked Questions
SIST EN 300 973 V7.0.1:2003 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "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)". This standard covers: Upgrade from Phase 2+ to Release 1998
Upgrade from Phase 2+ to Release 1998
SIST EN 300 973 V7.0.1:2003 is classified under the following ICS (International Classification for Standards) categories: 33.070.50 - Global System for Mobile Communication (GSM). The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN 300 973 V7.0.1:2003 is associated with the following European legislation: Standardization Mandates: T-172. When a standard is cited in the Official Journal of the European Union, products manufactured in conformity with it benefit from a presumption of conformity with the essential requirements of the corresponding EU directive or regulation.
SIST EN 300 973 V7.0.1:2003 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHP ID]D ±*RYRUVSRORYLþQRKLWURVWMR±
'HWHNWRUJRYRUQLKGHMDYQRVWL 9$' 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)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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
(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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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
(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
(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
(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
(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
(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
(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
(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
...