SIST ETS 300 581-4 E1:2003

• Abstract:

  ..

• 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 ETS 300 581-4 ed.1 (1995-12) - European digital cellular telecommunications system; Half rate speech; Part 4: Comfort noise aspects for the half rate speech traffic channels (GSM 06.22)

SIST ETS 300 581-4 E1:2003 is the Slovenian adoption of ETS 300 581-4 from the European Telecommunications Standards Institute (ETSI) for the European digital cellular telecommunications system, Global System for Mobile communications (GSM). It specifies the comfort noise aspects of half rate speech traffic channels (GSM 06.22), including how background acoustic noise is evaluated, encoded, transmitted, received and regenerated during discontinuous transmission (DTX) for mobile stations (MS) and base station systems (BSS).

What does SIST ETS 300 581-4 E1:2003 specify?

SIST ETS 300 581-4 E1:2003 gives the detailed requirements for comfort noise handling on GSM half rate speech traffic channels. In practice, it tells implementers how to keep background noise sounding natural when transmission pauses during DTX.

The document applies to MS that support the half rate speech traffic channel. On the network side, the receiver requirements are mandatory for BSS that support the channel, while transmitter requirements apply only where downlink DTX is used.

The document is organized into:

• Scope
• Normative references
• Definitions, symbols and abbreviations
• General principles
• Transmit (TX) side functions
• Receive (RX) side functions
• Computational details

What are the key requirements of SIST ETS 300 581-4 E1:2003?

SIST ETS 300 581-4 E1:2003 centers on preserving background noise perception when speech transmission stops and restarts. The main requirement is that the sender and receiver exchange and reuse comfort noise parameters so the listener hears stable synthetic noise instead of abrupt silence changes.

Implementation coverage

The standard makes the requirements mandatory for all GSM MS capable of supporting the half rate speech traffic channel. For BSS, the RX side requirements are mandatory, and TX side requirements are needed only when downlink DTX is used. This matters because it determines which parts of the codec and base station software must implement the procedures.

Transmit-side noise evaluation

Clause 5.1 defines how the TX side evaluates background acoustic noise from encoder parameters. It averages frame energy, autocorrelation values and the GS energy tweak parameter over recent frames marked with Voice Activity Detector (VAD) activity state. This gives the decoder a stable estimate of the noise level and spectrum before speech transmission ends.

SID frame handling

Clause 5.3 defines the Silence Descriptor (SID) frame used to carry comfort noise information. The SID frame uses the voiced-frame output format and a fixed SID codeword, and it replaces selected speech parameters with quantized values derived from the averaged noise estimates. In practice, this is the frame that tells the far end to start or refresh comfort noise generation.

TX-side encoder changes during SID generation

Clause 5.2 changes normal speech encoding behavior when a SID frame is being generated. It suppresses some normal speech coding steps, forces unvoiced mode, avoids fixed codebook search, and uses pseudo-random values for selected codebook indices. This simplifies SID generation and helps keep the comfort noise separate from normal speech coding.

Receive-side averaging and freezing

Clause 6.1 requires the RX side to keep the last seven speech frames worth of GS values in memory. When a valid SID frame arrives, those values are averaged, quantized and then frozen for the current comfort noise insertion period. That means the receiver can reconstruct a noise character that matches the recent transmit-side background.

Comfort noise generation and updating

Clause 6.2 says the decoder uses the GSM half rate speech decoder algorithm to synthesize the noise. Frame energy and LPC coefficients are interpolated between valid SID frames to avoid abrupt transitions, while the GSP0 codewords remain frozen during each insertion period. This is what makes the regenerated noise sound smooth rather than jumpy.

Computational reference

Clause 7 points implementers to an ANSI C source code description in GSM 06.06. That gives software teams a low-level implementation reference when coding or verifying the algorithm.

What terms does SIST ETS 300 581-4 E1:2003 define?

• frame - A 20 ms interval used by the half rate speech transcoder, also called a traffic frame.
• SID frame - A frame identified by the SID (Silence Descriptor) codeword and used to convey background noise information.
• SID codeword - The fixed bit pattern that marks a traffic frame as a SID frame.
• speech frame - A traffic frame that cannot be classified as a SID frame.
• VAD flag - The Voice Activity Detector flag used to mark whether speech activity is present.
• SP flag - The speech flag used in the encoder control flow.
• AFLAT - Autocorrelation Fixed Point LAttice Technique, used for vector quantization of LPC coefficients.
• BSS - Base Station System.

Who uses SIST ETS 300 581-4 E1:2003?

SIST ETS 300 581-4 E1:2003 is used by GSM codec designers, mobile station firmware engineers, and base station system developers. It is also relevant to test engineers and conformance labs that verify DTX behavior, SID frame handling, and comfort noise generation on half rate speech traffic channels.

Quality managers and buyers use it to check whether an MS or BSS implementation includes the required comfort noise behavior for the GSM half rate speech channel. Network and device integrators use it when they need consistent audio behavior during pauses in speech transmission.

Which standards are used with SIST ETS 300 581-4 E1:2003?

Reference	What it contributes
GSM 01.04 (ETR 100)	Abbreviations and acronyms used in the GSM series.
GSM 06.20 (ETS 300 581-2)	Half rate speech transcoding, including encoder and decoder processing used by this part.
GSM 06.41 (ETS 300 581-5)	Discontinuous Transmission (DTX), including when SID frames are sent and when comfort noise is updated.
GSM 06.42 (ETS 300 581-6)	Voice Activity Detector (VAD) behavior used to control speech and SID handling.
GSM 06.06 (ETS 300 581-7)	ANSI-C code for the GSM half rate speech codec, including the low-level computational description.

The foreword also places this document in the half rate speech series:

• GSM 06.02 - Part 1, half rate speech processing functions
• GSM 06.20 - Part 2, half rate speech transcoding
• GSM 06.21 - Part 3, substitution and muting of lost frames
• GSM 06.22 - Part 4, comfort noise aspects
• GSM 06.41 - Part 5, DTX
• GSM 06.42 - Part 6, VAD
• GSM 06.06 - Part 7, ANSI-C code
• GSM 06.07 - Part 8, test vectors

What does the SIST ETS 300 581-4 E1:2003 document contain?

SIST ETS 300 581-4 E1:2003 contains the rules and procedures for calculating comfort noise parameters, building SID frames, and regenerating comfort noise at the receiver. It includes the averaging formulas for frame energy, autocorrelation values and GS parameters, plus a simplified encoder block diagram for comfort noise insertion.

The document also contains table-based parameter settings for SID frame encoding and for comfort noise decoding, showing which codec parameters are replaced, frozen or interpolated. These tables are used for implementation and test verification rather than for manual calculation.

Clause 7 points to an ANSI C source code description for the computational details. That makes the document useful both for software development and for checking that a codec follows the specified GSM half rate speech behavior.

SLOVENSKI STANDARD
01-december-2003
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*60
European digital cellular telecommunications system; Half rate speech; Part 4: Comfort
noise aspects for the half rate speech traffic channels (GSM 06.22)
Ta slovenski standard je istoveten z: ETS 300 581-4 Edition 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 ETS 300 581-4
TELECOMMUNICATION November 1995
STANDARD
Source: ETSI TC-SMG Reference: DE/SMG-020622
ICS: 33.060.50
European digital cellular telecommunications system, Global System for Mobile communications
Key words:
(GSM)
European digital cellular telecommunications system;
Half rate speech
Part 4: Comfort noise aspects for the half rate
speech traffic channels
(GSM 06.22)
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
Tel.: [phone] - Fax: [phone]
*
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 1995. All rights reserved.

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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions, symbols and abbreviations.7
3.1 Definitions .7
3.2 Symbols .8
4 General.9
5 Functions on the transmit (TX) side .9
5.1 Background acoustic noise evaluation .9
5.2 Modification of the speech encoding algorithm during SID frame generation .11
5.3 SID-frame encoding.12
6 Functions on the receive (RX) side .12
6.1 Averaging of the GS parameters .12
6.2 Comfort noise generation and updating.13
7 Computational details.14
History.15

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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
Foreword
This European Telecommunication Standard (ETS) has been produced by the Special Mobile Group
(SMG) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS specifies the half rate speech traffic channels for the European digital cellular
telecommunications system. This ETS corresponds to GSM technical specification, GSM 06.22, version
4.1.1 and is part 4 of a multi-part ETS covering the half rate speech traffic channels as described below:
GSM 06.02 ETS 300 581-1: "European digital cellular telecommunications system;
Half rate speech Part 1: Half rate speech processing functions".
GSM 06.20 ETS 300 581-2: "European digital cellular telecommunications system;
Half rate speech Part 2: Half rate speech transcoding".
GSM 06.21 ETS 300 581-3: "European digital cellular telecommunications system;
Half rate speech Part 3: Substitution and muting of lost frames for half rate
speech traffic channels".
GSM 06.22 ETS 300 581-4: "European digital cellular telecommunications system;
Half rate speech Part 4: Comfort noise aspects for half rate speech traffic
channels".
GSM 06.41 ETS 300 581-5: "European digital cellular telecommunications system;
Half rate speech Part 5: Discontinuous Transmission (DTX) for half rate speech
traffic channels".
GSM 06.42 ETS 300 581-6: "European digital cellular telecommunications system;
Half rate speech Part 6: Voice Activity Detection (VAD) for half rate speech
traffic channels".
GSM 06.06 ETS 300 581-7: "European digital cellular telecommunications system;
Half rate speech Part 7: ANSI-C code for the GSM half rate speech codec".
GSM 06.07 ETS 300 581-8: "European digital cellular telecommunications system;
Half rate speech Part 8: Test vectors for the GSM half rate speech codec".
NOTE: TC-SMG has produced documents which give the technical specifications for the
implementation of the European digital cellular telecommunications system.
Historically, these documents have been identified as GSM Technical Specifications
(GSM-TS). These TSs may have subsequently become Interim European
Telecommunication Standards (I-ETSs), (Phase 1), or European Telecommunication
Standards (ETSs), (Phase 2), whilst others may become ETSI Technical Reports
(ETRs).
Transposition dates
Date of adoption of this ETS: 27 October 1995
Date of latest announcement of this ETS (doa): 28 February 1996
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 August 1996
Date of withdrawal of any conflicting National Standard (dow): 31 August 1996

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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
1 Scope
This European Telecommunication Standard (ETS) gives the detailed requirements for the correct operation
of the background acoustic noise evaluation, noise parameter encoding/decoding and comfort noise
generation in GSM Mobile Stations (MS)s and Base Station Systems (BSS)s during Discontinuous
Transmission (DTX) on half rate speech traffic channels.
The requirements described in this ETS are mandatory for implementation in all GSM MSs capable of
supporting the half rate speech traffic channel.
The receiver requirements are mandatory for implementation in all GSM BSSs capable of supporting the
half rate speech traffic channel, the transmitter requirements are only for those where downlink DTX will
be used.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] GSM 01.04 (ETR 100): "European digital cellular telecommunication system
(Phase 2); Abbreviations and acronyms".
[2] GSM 06.20 (ETS 300 581-2): "European digital cellular telecommunications
system; Half rate speech Part 2: Half rate speech transcoding".
[3] GSM 06.41 (ETS 300 581-5): "European digital cellular telecommunications
system; Half rate speech Part 5: Discontinuous transmission (DTX) for half rate
speech traffic channels".
[4] GSM 06.42 (ETS 300 581-6): "European digital cellular telecommunications
system; Half rate speech Part 6: Voice Activity Detector (VAD) for half rate
speech traffic channels".
[5] GSM 06.06 (ETS 300 581-7): "European digital cellular telecommunications
system; Half rate speech Part 7: ANSI-C code for the GSM half rate speech
codec".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purpose of this ETS, the following definition apply.
frame: Time interval of 20 ms corresponding to the time segmentation of the half rate speech transcoder,
also used as a short term for a traffic frame.
SID frame: Rame characterised by the SID (Silence Descriptor) codeword. It conveys information on the
acoustic background noise.
SID codeword: Fixed bit pattern for labelling a traffic frame as a SID frame.
SID field: The bit positions of the SID codeword within a SID frame.
speech frame: Traffic frame that cannot be classified as a SID frame.
VAD flag: Voice Activity Detector flag.
SP flag: SPeech flag.
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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
W(Z): Spectral weighting filter of the GSM half rate speech codec.
H(Z): Combination of the short term (spectral) filter A(z) and the spectral weighting filter W(z).
Other definition of terms used in this ETS can be found in GSM 06.20 (ETS 300 581-2) [2] and
GSM 06.41 (ETS 300 581-5) [3]. The overall operation of DTX is described in
GSM 06.41 (ETS 300 581- 5) [3].
3.2 Symbols
For the purpose of this ETS, the following symbols apply.
GS Energy tweak parameter.
R0 Frame energy value.
R(i) Unquantised (normalised) autocorrelation sequence.
r Optimal reflection coefficient.
j
b
SUM ( x(n) ) = x(a) + x(a+1) + . + x(b-1) + x(b);  (Accumulation)
n=a
GSP0 codeword Vector quantization index, joint vector quantization of the parameters GS and
P0.
P0 Power contribution of the first excitation vector as a fraction of the total
excitation power at a subframe.
3.3 Abbreviations
For the purpose of this ETS, the following abbreviations apply:
AFLAT Autocorrelation Fixed Point LAttice Technique (used in the GSM half rate
speech codec for the vector quantization of the LPC coefficients)
BSS Base Station System
DTX Discontinuous Transmission
ETS European Telecommunication Standard
GSM Global System for Mobile communications
MS Mobile Station
SID SIlence Descriptor
RX Receive
TX Transmit
VAD Voice Activity Detector
VQ Vector Quantization
For abbreviations not given in this subclause, see GSM 01.04 (ETR 100) [1].

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ETS 300 581-4: November 1995 (GSM 06.22 version 4.1.1)
4 General
A problem when using DTX is that the background acoustic noise, which is transmitted together with the
speech, would disappear when the radio transmission is switched off, resulting in a modulation of the
background noise. Since the DTX switching can take place rapidly, it has been found that this effect may be
annoying for the listener, especially in a car environment with high background noise levels. In bad cases,
the speech may be hardly intelligible.
This ETS specifies a solution to overcome this problem by generating s
...