3rd Generation Partnership Project;

Technical Specification Group Services and System Aspects;

Mandatory speech CODEC speech processing functions;
V10.0.0 (2011-03)
AMR speech CODEC; General description
Technical Specification
(Release
10)

3GPP TS 26.071

The present document has been developed within the 3rd Generation Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP.
The present document has not been subject to any approval process by the 3GPP Organizational Partners and shall not be implemented.
This Specification is provided for future development work within 3GPP only. The Organizational Partners accept no liability for any use of this
Specification.
Specifications and reports for implementation of the 3GPP TM system should be obtained via the 3GPP Organizational Partners' Publications Offices.

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Keywords
GSM, UMTS, codec, LTE

3GPP
Postal address
3GPP support office address
650 Route des Lucioles - Sophia Antipolis
Valbonne - FRANCE
Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16

Internet
http://www.3gpp.org

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.
2011, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC).
All rights reserved.
UMTS is a Trade Mark of ETSI registered for the benefit of its members
3GPP is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners
LTE is a Trade Mark of ETSI currently being registered for the benefit of its Members and of the 3GPP
Organizational Partners
GSM and the GSM logo are registered and owned by the GSM Association

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Contents
Foreword..........................................................................................................................................................
1

Scope......................................................................................................................................................

References..............................................................................................................................................

Definitions and abbreviations.................................................................................................................

3.1

Abbreviations.......................................................................................................................................................

General...................................................................................................................................................

Adaptive Multi-Rate speech codec transcoding functions......................................................................

Adaptive Multi-Rate speech codec ANSI C-code...................................................................................

Adaptive Multi-Rate speech codec test vectors......................................................................................

Adaptive Multi-Rate speech codec source controlled rate operation......................................................

Adaptive Multi-Rate speech codec voice activity detection...................................................................

10

Adaptive Multi-Rate speech codec comfort noise insertion..................................................................

11

Adaptive Multi-Rate speech codec error concealment of lost frames...................................................

12

Adaptive Multi-Rate speech codec frame structure..............................................................................

13

Adaptive Multi-Rate speech codec interface to RAN...........................................................................

14

Adaptive Multi-Rate speech codec performance characterisation.........................................................

Annex A (informative):

Change history..............................................................................................

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Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.

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Scope

The present document is an introduction to the speech processing parts of the narrowband telephony speech service
employing the Adaptive Multi-Rate (AMR) speech coder. A general overview of the speech processing functions is
given, with reference to the documents where each function is specified in detail.

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. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.

[1]

GSM 03.50: "Digital cellular telecommunications system (Phase 2); Transmission planning
aspects of the speech service in the GSM Public Land Mobile Network (PLMN) system".

[2]

3GPP TS 26.090: "Transcoding functions".

[3]

3GPP TS 26.073: "Adaptive Multi-Rate (AMR); ANSI C source code".

[4]

3GPP TS 26.074: "Adaptive Multi-Rate (AMR); Test sequences".

[5]

3GPP TS 26.093: "Source Controlled Rate operation".

[6]

3GPP TS 26.094: "AMR Speech Codec; Voice Activity Detector".

[7]

3GPP TS 26.092: "Mandatory Speech Codec speech processing functions; AMR Speech Codec;
Comfort noise aspects".

[8]

3GPP TS 26.091: "Mandatory Speech Codec speech processing functions; AMR Speech Codec;
Error concealment of lost frames".

[9]

3GPP TS 26.101: "Frame Structure".

[10]

3GPP TS 26.102: "AMR Speech Codec; Interface to Iu snd Uu".

[11]

3GPP TS 26.901: "AMR wideband speech codec feasibility study report ".

[12]

ITU-T Recommendation G.711: "Pulse code modulation (PCM) of voice frequencies".

[13]

ITU-T Recommendation H.324: "Terminal for low bit-rate multimedia communication".

Definitions and abbreviations

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3.1 Abbreviations
For the purposes of this TS, the following abbreviations apply:
ACELP
AMR
BFI
CHD
CHE
GSM
ITU-T
PCM
PLMN
PSTN
RX
SCR
SPD
SPE
TC
TX
UE

Algebraic Code Excited Linear Prediction

Adaptive Multi-Rate
Bad Frame Indication
Channel Decoder
Channel Encoder
Global System for Mobile communications
International Telecommunication Union Telecommunication standardisation sector (former
CCITT)
Pulse Code Modulation
Public Land Mobile Network
Public Switched Telephone Network
Receive
Source Controlled Rate
SPeech Decoder
SPeech Encoder
Transcoder
Transmit
User Equipment (terminal)

General

The AMR speech coder consists of the multi-rate speech coder, a source controlled rate scheme including a voice
activity detector and a comfort noise generation system, and an error concealment mechansim to combat the effects of
transmission errors and lost packets.
The multi-rate speech coder is a single integrated speech codec with eight source rates from 4.75 kbit/s to 12.2 kbit/s,
and a low rate background noise encoding mode. The speech coder is capable of switching its bit-rate every 20 ms
speech frame upon command.
A reference configuration where the various speech processing functions are identified is given in Figure 1. In this
figure, the relevant specifications for each function are also indicated.
In Figure 1, the audio parts including analogue to digital and digital to analogue conversion are included, to show the
complete speech path between the audio input/output in the User Equipment (UE) and the digital interface of the
network. The detailed specification of the audio parts is not within the scope of the present document. These aspects are
only considered to the extent that the performance of the audio parts affect the performance of the speech transcoder.

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GSM 06.82.AMR

BSS side only

Voice
Activity
Detector

GSM 06.60.AMR

3
VAD

8bit / A-law
to
13-bit
uniform

GSM 06.81.AMR

SP
flag

GSM 06.60.AMR
6

DTX
Control
and
Operation

Speech
Encoder

4
LPF

A/D

MS side only

Speech frame
Info.
bits

GSM 06.62.AMR

GSM 03.50
Comfort
Noise
TX
Functions

TRANSMIT SIDE

5
SID frame

GSM 06.81.AMR

GSM 06.61.AMR

Info.
bits

Speech
frame
substitution

8
BFI

BSS side only

13-bit
uniform
to
8bit / A-law

GSM 06.60.AMR

9
SID
10
TAF
11

DTX
Control
and
Operation

Speech
Decoder

D/A

Speech frame
GSM 06.62.AMR

GSM 06.60.AMR

LPF

MS side only
Comfort
Noise
RX
Functions

GSM 03.50

RECEIVE SIDE

SID frame

Figure 1: Overview of audio processing functions

1) 8-bit A-law or -law PCM (ITU-T Recommendation G.711 [12] ), 8 000 samples/s;
2) 13-bit uniform PCM, 8 000 samples/s;
3) Voice Activity Detector (VAD) flag;
4) Encoded speech frame, 50 frames/s, number of bits/frame depending on the AMR codec mode;
5) SIlence Descriptor (SID) frame;
6) TX_TYPE, 2 bits, indicates whether information bits are available and if they are speech or SID information;
7) Information bits delivered to the 3G AN;
8) Information bits received from the 3G AN;
9) RX_TYPE, the type of frame received quantized into three bits.

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Adaptive Multi-Rate speech codec transcoding

functions

The adaptive multi-rate speech codec is described in [2]. The technical content is identical to that of 3GPP TS 26.090.
As shown in Figure 1, the speech encoder takes its input as a 13-bit uniform Pulse Code Modulated (PCM) signal either
from the audio part of the UE or on the network side, from the Public Switched Telephone Network (PSTN) via an 8-bit
A-law or -law to 13-bit uniform PCM conversion. The encoded speech at the output of the speech encoder is
packetized and delivered to the network interface. In the receive direction, the inverse operations take place.
The detailed mapping between input blocks of 160 speech samples in 13-bit uniform PCM format to encoded blocks (in
which the number of bits depends on the presently used codec mode) and from these to output blocks of 160
reconstructed speech samples is described in [2]. The coding scheme is Multi-Rate Algebraic Code Excited Linear
Prediction. The bit-rates of the source codec are listed in Table 1.
An AMR speech codec capable UE shall support all source rates listed in Table 1.
Table 1: Source codec bit-rates for the AMR codec.
Codec mode
AMR_12.20
AMR_10.20

Source codec bit-rate

12,20 kbit/s (GSM EFR)
10,20 kbit/s

AMR_7.95

7,95 kbit/s

AMR_7.40

7,40 kbit/s (IS-641)

AMR_6.70

6,70 kbit/s (PDC-EFR)

AMR_5.90

5,90 kbit/s

AMR_5.15

5,15 kbit/s

AMR_4.75

4,75 kbit/s

AMR_SID

1,80 kbit/s (see note 1)

NOTE 1: Assuming SID frames are continously transmitted

NOTE 2: GSM-EFR is the 3GPP TS 26.090 Enhanced Full Rate Speech Codec (also
identical to the TIA TDMA-US1 Enhanced speech codec)
NOTE 3: IS-641is the TIA/EIA IS-641 TDMA Enhanced Full Rate Speech Codec
NOTE 4: PDC-EFR is the ARIB 6.7 kbit/s Enhanced Full Rate Speech Codec

Adaptive Multi-Rate speech codec ANSI C-code

The ANSI-C code of the speech codec, VAD and CNG system are described in [3]. The ANSI C-code is mandatory. The
ANSI C-code is identical to that of 3GPP TS 26.073 [3].

Adaptive Multi-Rate speech codec test vectors

A set of digital test sequences is specified in [4], thus enabling the verification of compliance, i.e. bit-exactness, to a
high degree of confidence. The test vectors are identical to those of 3GPP TS 26.074 [4].
The test sequences are defined separately for:
The speech codec described in [2],
The VAD described in [6],
The CN generation described in [7].
The adaptive multi-rate speech transcoder, VAD, SCR system and comfort noise parts of the audio processing functions
(see Figure 1) are defined in bit exact arithmetic. Consequently, they shall react on a given input sequence always with

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the corresponding bit exact output sequence, provided that the internal state variables are also always exactly in the
same state at the beginning of the test.
The input test sequences provided shall force the corresponding output test sequences, provided that the tested modules
are in their home-state when starting.
The modules may be set into their home states by provoking the appropriate homing-functions.
NOTE:

This is normally done during reset (initialisation of the codec).

Special inband signalling frames (encoder-homing-frame and decoder-homing-frame) described in [2]have been defined
to provoke these homing-functions also in remotely placed modules.
At the end of the first received homing frame, the audio functions that are defined in a bit exact way shall go into their
predefined home states. The output corresponding to the first homing frame is dependent on the codec state when the
frame was received. Any consecutive homing frames shall produce corresponding homing frames at the output.

Adaptive Multi-Rate speech codec source controlled

rate operation

The source controlled rate operation of the adaptive multi-rate speech codec is defined in [5].
During a normal telephone conversation, the participants alternate so that, on the average, each direction of transmission
is occupied about 50 % of the time. Source controlled rate (SCR) is a mode of operation where the speech encoder
encodes speech frames containing only background noise with a lower bit-rate than normally used for encoding speech.
A network may adapt its transmission scheme to take advantage of the varying bit-rate. This may be done for the
following two purposes:
1) In the UE, battery life will be prolonged or a smaller battery could be used for a given operational duration.
2) The average required bit-rate is reduced, leading to a more efficient transmission with decreased load and hence
increased capacity.
The following functions are required for the source controlled rate operation:
a Voice Activity Detector (VAD) on the TX side;
evaluation of the background acoustic noise on the TX side, in order to transmit characteristic parameters to
the RX side;
generation of comfort noise on the RX side during periods when no normal speech frames are received.
The transmission of comfort noise information to the RX side is achieved by means of a Silence Descriptor (SID)
frame, which is sent at regular intervals.

Adaptive Multi-Rate speech codec voice activity

detection

The adaptive multi-rate VAD function is described in [6].

The input to the VAD is the input speech itself together with a set of parameters computed by the adaptive multi-rate
speech encoder. The VAD uses this information to decide whether each 20 ms speech coder frame contains speech or
not.
The VAD algorithm is described in [6], and the corresponding C code is defined in [3]. The verification of compliance
to [6]. is achieved by use of digital test sequences applied to the same interface as the test sequences for the speech
codec.

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Adaptive Multi-Rate speech codec comfort noise

insertion

The adaptive multi-rate comfort noise insertion function is described in [7].

When speech is absent, the synthesis in the speech decoder is different from the case when normal speech frames are
received. The synthesis of an artificial noise based on the received non-speech parameters is termed comfort noise
generation.
The comfort noise generation process is as follows:
the evaluation of the acoustic background noise in the transmitter;
the noise parameter encoding (SID frames) and decoding, and
the generation of comfort noise in the receiver.
The comfort noise processes and the algorithm for updating the noise parameters during speech pauses are defined in
detail in [7], and the corresponding C code is defined in [3]. The comfort noise mechanism is based on the adaptive
multi-rate speech codec defined in [2].

11

Adaptive Multi-Rate speech codec error concealment

of lost frames

The adaptive multi-rate speech codec error concealment of lost frames is described in [8].
Frames may be lost due to transmission errors or frame stealing in a wireless environment. Actions which shall be taken
in these cases, both for lost speech frames and for lost SID frames are described in [8]. Error concealment actions shall
be used also in the case of lost speech packets in the transport network. The methods described in [8] may with some
modifications be used as a basis for such actions.
In order to mask the effect of isolated lost frames, the speech decoder shall be informed and the error concealment
actions shall be initiated, whereby a set of predicted parameters are used in the speech synthesis. Insertion of speech
signal independent silence frames is not allowed. For several subsequent lost frames, a muting technique shall be used
to indicate to the listener that transmission has been interrupted.

12

Adaptive Multi-Rate speech codec frame structure

The adaptive multi-rate speech frame structure is described in [9]. The output interface format from the encoder and
input interface format to the decoder is divided into two parts; the core speech data part, which is the speech coded bits,
and the other part is an additional data part with mode information.
The interface format described in [9] is termed AMR interface format 1 (AMR IF1).
Annex A of [9] describes an octet aligned frame format which shall be used in applications requiring octet alignment,
such as for ITU-T Recommendation H.324 [13]. This format is termed AMR interface format 2 (AMR IF2).

13

Adaptive Multi-Rate speech codec interface to RAN

The adaptive multi-rate speech service interface to RAN is described in [10].

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Adaptive Multi-Rate speech codec performance

characterisation

The adaptive multi-rate speech channel performance characterisation is described in [11].

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Annex A (informative):
Change history
Document history
V.0.1.0

March 1999

First Draft

V.0.1.1

April 1999

References changed

V.1.0.0

April 22, 1999

Editorial changes

V.2.0.0

June 15, 1999

Minor Editorial changes

V.3.0.0

June 22, 1999

Approved at 3GPP TSG SA#4 Plenary meeting

V.3.0.1

August 22, 1999

Reformatted
Change history

Date
03-2001
06-2002
12-2004
06-2007
07-2007
12-2008
12-2009
03-2011

TSG #
11
16
26
36
42
46
51

TSG Doc.

CR

Rev Subject/Comment
Rel-4 version
Rel-5 version
Rel-6 version
Rel-7 version
Correction to version shown on cover
Rel-8 version
Rel-9 version
Rel-10 version

3GPP

Old
4.0.0
5.0.0
6.0.0
7.0.0
7.0.1
8.0.0
9.0.0

New
4.0.0
5.0.0
6.0.0
7.0.0
7.0.1
8.0.0
9.0.0
10.0.0