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TECHNICAL SPECIFICATION
Speech and multimedia Transmission Quality (STQ);
Methods for reproducing reverberation
for communication device measurements
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2 ETSI TS 103 557 V1.1.1 (2018-12)
Reference
DTS/STQ-263
Keywords
quality, reverberation, simulation, speech,
terminal, testing
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3 ETSI TS 103 557 V1.1.1 (2018-12)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
Introduction . 4
1 Scope . 5
2 References . 5
2.1 Normative references . 5
2.2 Informative references . 5
3 Definitions of terms, symbols and abbreviations . 6
3.1 T erms . 6
3.2 Symbols . 6
3.3 Abbreviations . 6
4 Rationale . 7
5 Room simulation in Sending . 7
5.1 Impulse Response Measurement . 7
5.1.1 Microphone setup . 7
5.1.1.1 Fixed Microphone setup . 7
5.1.1.2 Flexible Microphone setup . 7
5.1.2 Sound source . 7
5.1.3 Measurement procedure . 8
5.2 Loudspeaker setup for reproducing reverberation based on the fixed microphone setup . 8
5.2.1 Introduction and System Overview . 8
5.2.2 Preparations . 9
5.2.2.1 Separation of impulse responses . 9
5.2.2.2 Delay and level adjustment . 10
5.2.3 Test room requirements . 11
5.2.4 Equalization and calibration . 11
5.2.5 Accuracy of the reproduction arrangement . 12
5.2.5.1 Evaluation parameters . 12
5.2.5.2 Reverberation time . 12
5.2.5.3 Clarity . 12
5.2.5.4 Direct-to-Reverberant Energy Ratio . 12
5.2.5.5 Coherence. 12
5.3 Loudspeaker setup for reproducing reverberation based on the flexible microphone setup . 13
5.4 Impulse response database and signal generation . 13
5.5 Validation and examples . 13
5.5.1 Reproduction of room acoustical parameters . 13
5.5.2 Application examples . 17
Annex A (normative): Impulse Response Database . 19
A.1 Fixed microphone setup . 19
History . 20
ETSI
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4 ETSI TS 103 557 V1.1.1 (2018-12)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables 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 ETSI 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 (https://ipr.etsi.org/).
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 ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Speech and multimedia
Transmission Quality (STQ).
The present document is to be used in conjunction with:
• ETSI TS 103 224 [1] series: "A sound field reproduction method for terminal testing including a background
noise database".
The present document describes a sound field recording and reproduction technique which can be applied for all types
of terminals but is especially suitable for modern multi-microphone terminals including array techniques. While [1]
focuses on background noise, the present document considers the reproduction of reverberation.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
Many devices that employ microphones to pick up speech signals are used in a hands-free manner. Since there is
usually a larger distance between the talker and the device, the microphone signals contain a significant amount of noise
and reverberation.
This includes, e.g. phones in hands-free mode, group-audio terminals or smart speakers with speech recognition
capabilities as well as terminals in handset or headset mode. Note that the same issues can also arise for hand-held
devices depending on the acoustic conditions, see [i.1].
Testing of these devices requires a realistic reproduction of both the noise as well as the reverberation in a defined and
reproducible manner. For background noise reproduction, ETSI has standardized a reproduction method (with an
accompanying database of background noise signals) in ETSI TS 103 224 [1].
ETSI
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5 ETSI TS 103 557 V1.1.1 (2018-12)
1 Scope
The present document describes a methodology for recording and reproducing different room characteristics and
realistic reverberation under conditions that are well-defined and tailored for a calibrated setup in a lab environment.
The individual aspects of the description are:
• Measurement of room impulse responses.
• Processing of test signals.
• Loudspeaker setup, calibration and equalization.
The methodology is fundamentally designed for use without access to internals of the Device Under Test (DUT),
e.g. the exact positions and orientations of the device's microphones or the unprocessed microphone signals. The
methodology is intended to be used for performance evaluation of all types of devices where the room characteristics
may impact the performance.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 103 224: "Speech and multimedia Transmission Quality (STQ); A sound field
reproduction method for terminal testing including a background noise database".
[2] Recommendation ITU-T P.58: "Head and Torso Simulator for Telephonometry".
[3] N. Xiang: "Evaluation of reverberation times using a nonlinear regression approach" in Journal of
the Acoustical Society of America Vol. 98, 1995.
[4] Recommendation ITU-T P.56: "Objective measurement of active speech level".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] M. Jeub, M. Schäfer, H. Krüger, C. Nelke, C. Beaugeant and P. Vary: "Do We Need
Dereverberation for Hand-Held Telephony?", International Congress on Acoustics (ICA), Sydney,
2010.
ETSI
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6 ETSI TS 103 557 V1.1.1 (2018-12)
[i.2] Recommendation ITU-T P.341 (03/2011): "Transmission characteristics for wideband digital
loudspeaking and hands-free telephony terminals".
[i.3] ISO 3382-1: "Measurement of room acoustic parameters -- Part 1: Performance spaces".
[i.4] Recommendation ITU-T P.501: "Test signals for use in telephonometry".
[i.5] ETSI TS 103 738: "Speech and multimedia Transmission Quality (STQ); Transmission
requirements for narrowband wireless terminals (handsfree) from a QoS perspective as perceived
by the user".
[i.6] ETSI TS 103 740: "Speech and multimedia Transmission Quality (STQ); Transmission
requirements for wideband wireless terminals (handsfree) from a QoS perspective as perceived by
the user".
3 Definition of terms, symbols and abbreviations
3.1 Terms
Void.
3.2 Symbols
For the purposes of the present document, the following symbols apply:
Clarity with cut-off time
Sampling frequency
Reverberant components of the impulse response to microphone
ℎ Impulse response to microphone
ℎ Impulse response to the microphone closest to the HATS
ℎ Direct path component of the impulse response to microphone ,
Length of the impulse response
Number of microphones
Reverberation time
Source signal
Cut-off time for clarity (50 ms for speech, 80 ms for music)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
DRR Direct-to-Reverberant energy Ratio
DUT Device Under Test
FFT Fast Fourier Transform
HATS Head And Torso Simulator
LRC Lip Ring Centre
MLS Maximum Length Sequence
SFR Send Frequency Response
SLR Send Loudness Rating
SNR Signal-to-Noise Ratio
ETSI
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7 ETSI TS 103 557 V1.1.1 (2018-12)
4 Rationale
Including reverberation in a realistic manner is of paramount importance for accurate testing of, e.g. phones in hands-
free mode, group-audio terminals or smart speakers with speech recognition capabilities. While it is possible to test this
simply by using the device in a reverberant room, the present document introduces an alternative approach that is based
on the explicit reproduction of the reverberant sound field at several microphone positions.
The present method does not require many rooms or variable acoustics setups for testing multiple acoustic conditions.
The reverberant sound field can both be measured directly in a reverberant room or it can be calculated based on a
database of impulse responses that is provided in combination with the present document.
NOTE 1: The room acoustics has an impact on three transmission paths that could be considered from a
measurement perspective:
from the mouth of the user to the microphone(s) of the DUT (Sending);
from the loudspeaker(s) of the DUT to the ears of the user (Receiving);
from the loudspeaker(s) of the DUT to the microphone(s) of the DUT (Echo-path).
NOTE 2: The methodology described in the present document is intended for the first scenario. Although it might
be applicable to the other scenarios as well (possibly with modifications), this has not been verified yet
and is subject to further study.
5 Room simulation in Sending
5.1 Impulse Response Measurement
5.1.1 Microphone setup
5.1.1.1 Fixed Microphone setup
A fixed microphone setup should be used for DUTs with smaller form factors (e.g. mobile phones in hands-free
operation). The microphone setup shall consist of =8 microphones and conform to the description in ETSI
TS 103 224 [1] (see clause 5, "Recording Arrangement"). Since this setup is device-independent, no new impulse
response measurements are necessary when testing a new device.
5.1.1.2 Flexible Microphone setup
For larger DUTs, a flexible microphone setup with a use-case dependent number of microphones shall be used. The
microphone setup shall conform to the description in ETSI TS 103 224 [1] (see clause 7, "Generalization of the method
for a more flexible loudspeaker and microphone arrangement"). Since this setup is device-dependent, testing a new
device requires new impulse response measurements.
5.1.2 Sound source
Since the testing scenario consists of a human talker in a reverberant environment, a HATS with an equalized artificial
mouth according to Recommendation ITU-T P.58 [2] shall be used for sound generation. This applies to measurement
of impulse responses as well as to recording of reverberant speech signals.
ETSI
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8 ETSI TS 103 557 V1.1.1 (2018-12)
5.1.3 Measurement procedure
There exist different possibilities for measuring impulse responses, e.g. using Maximum Length Sequences (MLS) or
using swept-sines (sweeps). The advantage of sweeps is that non-linearities can easily be observed and that the SNR in
lower frequencies is higher than with MLS. Using logarithmic sweeps is therefore recommended for system
identification. The sweep should cover a frequency range from 20 Hz to 20 kHz and the length of the sweep should be
chosen in such a way that no significant components of the impulse response are truncated. Accordingly, a sweep length
of at least 2 seconds should be used for typical rooms while larger rooms might need longer sweeps. While the sweep
can be used directly as the measurement signal, it is recommended to construct the measurement signal from the
individual sweep by repeating it at least five times. If the repetition is used, the determination of the impulse response
should be based on an averaging of all but the first sweep period. The first period is discarded to avoid transient effects
and the averaging should be performed in the time domain.
5.2 Loudspeaker setup for reproducing reverberation based on
the fixed microphone setup
5.2.1 Introduction and System Overview
In order to correctly reproduce the sound field in a reverberant room, the setup d
...