ETSI TS 103 224 V1.5.1 (2020-03)

ETSI TS 103 224 V1.5.1 (2020-03)






TECHNICAL SPECIFICATION
Speech and multimedia Transmission Quality (STQ);
A sound field reproduction method for terminal testing
including a background noise database

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2 ETSI TS 103 224 V1.5.1 (2020-03)



Reference
RTS/STQ-289
Keywords
noise, quality, speech, terminal
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3 ETSI TS 103 224 V1.5.1 (2020-03)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definition of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Symbols . 9
3.2 Abbreviations . 9
4 Methods for realistic sound reproduction . 9
5 Recording arrangement . 9
5.0 General . 9
5.1 Microphone array setup . 10
5.1.1 Principle limitations . 10
5.1.2 Microphone calibration . 10
5.2 Microphone array setup for handset-type and headset terminals. 10
5.3 Microphone array setup for hands-free terminals . 11
5.4 Microphone array setup for binaural applications . 12
6 Loudspeaker setup for background noise simulation . 13
6.0 General setup . 13
6.1 Test room requirements . 14
6.2 Equalization and calibration . 15
6.2.0 Overview of the equalization procedure . 15
6.2.1 Separate level adjustment for each loudspeaker . 15
6.2.2 System identification . 15
6.2.3 Pre-processing of the impulse responses . 16
6.2.4 Calculation of the inversion filters . 18
6.2.4.0 Overview . 18
6.2.4.1 Inversion procedure . 18
6.2.4.2 Different microphones for different frequency bands . 20
6.2.4.3 Search for the optimum regularization factor . 20
6.2.4.3.0 Introduction . 20
6.2.4.3.1 Basic methodology to find the optimum regularization factor . 20
6.2.4.3.2 Extended methodology to find the optimum regularization factor for frequencies above 2 kHz . 22
6.2.5 First test of equalization and filter adjustment for inversion error compensation . 24
6.2.6 Accuracy of the equalization . 25
6.3 Accuracy of the reproduction arrangement . 25
6.3.0 Introduction. 25
6.3.1 Comparison between original sound field and simulated sound field . 25
6.3.2 Impact of handset positioner and phone on the simulated sound field . 27
6.3.3 Comparison of terminal performance in the original sound field and the simulated sound field . 28
6.3.3.1 Introduction . 28
6.3.3.2 Background noise transmission . 29
6.3.3.2.0 Validation Procedure . 29
6.3.3.2.1 Handset . 29
6.3.3.2.2 Handheld Hands-free . 33
6.3.3.2.3 Desktop Hands-Free . 34
6.3.3.3 S-/N-/G-MOS Analysis according to ETSI TS 103 106 . 34
6.3.3.3.1 Handset . 34
ETSI

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4 ETSI TS 103 224 V1.5.1 (2020-03)
6.3.3.3.2 Hands-free . 36
7 Generalization of the method for a more flexible loudspeaker and microphone arrangement. 37
7.0 Introduction . 37
7.1 Loudspeaker configuration . 37
7.2 Microphone setup . 37
7.3 Background noise recordings and reference noise . 38
7.4 Equalization and calibration . 38
7.5 Accuracy of the equalization . 39
7.6 Example use case: equalization inside a vehicle . 39
7.6.0 Introduction. 39
7.6.1 Loudspeaker configuration . 39
7.6.2 Microphone setup . 39
7.6.3 Equalization . 39
8 Background noise database . 40
8.0 Introduction . 40
8.1 Reference noise recording . 40
8.2 Background noise signals for terminal testing. 40
8.3 Background noise signals for binaural applications . 43
8.4 Background noise signals in a home-like test environment . 44
Annex A (informative): Home-like test environment . 47
History . 49

ETSI

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5 ETSI TS 103 224 V1.5.1 (2020-03)
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 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. The present
document provides an additional simulation technique which can be used instead of the part 1 of ETSI multi-part
deliverable ES/EG 202 396 "Speech quality performance in the presence of background noise", as identified below:
• ETSI ES 202 396-1: "Background noise simulation technique and background noise database" [i.7];
• ETSI EG 202 396-2: "Background noise transmission - Network simulation - Subjective test database and
results" [i.8];
• ETSI EG 202 396-3: "Background noise transmission - Objective test methods" [i.9].
The background noise simulation can be used in conjunction with the objective test methods as described in ETSI
EG 202 396-3 [i.9] and ETSI TS 103 106 [i.10].
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.
ETSI

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6 ETSI TS 103 224 V1.5.1 (2020-03)
Introduction
Background noise is present in most of the conversations today. Background noise may impact the speech
communication performance of terminal and network equipment significantly. Therefore testing and optimization of
such equipment is necessary using realistic background noises. Furthermore reproducible conditions for the tests are
required which can be guaranteed only under lab type conditions. Since modern terminals incorporate more advanced
noise cancellation techniques, such as multi-microphone based noise cancellation, the use of microphone-array
recording techniques and more realistic noise field simulations (compared to the method described in ETSI
ES 202 396-1 [i.7]) are required.
The present document addresses this topic by specifying a methodology for recording and playback of realistic
background noise fields under conditions that are well-defined and able to be calibrated in a lab type environment.
Furthermore a database with real background noises is included.
ETSI

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7 ETSI TS 103 224 V1.5.1 (2020-03)
1 Scope
The quality of background noise transmission is an important factor, which significantly contributes to the perceived
overall quality of speech. Terminals, networks, and system configurations including wideband, superwideband, and
fullband speech services can be greatly improved with a proper design of terminals and systems in the presence of
background noise. The present document:
• describes a sound field simulation technique allowing to simulate the real environment using realistic
background noise scenarios for laboratory use;
• contains a database including relevant background noise samples for subjective and objective evaluation.
The present document describes the recording technique used for the sound field simulation, the loudspeaker setup, and
the loudspeaker calibration and equalization procedures. Furthermore the present document specifies the test room
requirements for laboratory conditions.
The simulation environment specified can be used for the evaluation and optimization of terminals and of complex
configurations including terminals, networks and others. The main application areas are: outdoor, office, home and car
environment.
The setup and database as described in the present document are applicable for:
• Objective performance evaluation of terminals in different (simulated) background noise environments.
• Speech processing evaluation by using the pre-processed speech signals in the presence of background noise,
recorded by a terminal.
• Subjective evaluation of terminals by performing conversational tests, specific double talk tests, or talking and
listening tests in the presence of background noise.
• Subjective evaluation in third party listening tests by recording the speech samples of terminals in the presence
of background noise.
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.
Not applicable.
ETSI

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8 ETSI TS 103 224 V1.5.1 (2020-03)
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] Berkhout A. J., de Vries D., & Vogel, P.: "Acoustic control by wave field synthesis", J. Acoust.
Soc. Am., p. 2764-2778, Mai 1993.
[i.2] Gerzon, M. A.: "Periphony: With-Height Sound Production", Journal of the Audio Engineering
Society 21, 1973.
[i.3] Ward D. B., Abhayapala T. D.: "Reproduction of a Plane-Wave Sound Field Using an Array of
Loudspeakers", IEEE transactions on speech and audio processing, Vol. 9, No.6, p. 697-707,
September 2001.
[i.4] Kirkeby O., Nelson P. A., Orduna-Bustamante F., Hamada H.: "Local sound field reproduction
using digital signal processing", J. Acoust. Soc. Am. 100(3), p. 1584-1593, September 1996.
[i.5] Kirkeby O., Nelson P. A., Hamada H., Orduna-Bustamante F.: "Fast Deconvolution of
Multichannel Systems Using Regularization", IEEE transactions on speech and audio processing,
VOL. 6, NO. 2, p. 189-195, March 1998.
[i.6] Recommendation ITU-T P.58: "Head and Torso Simulator for Telephonometry".
[i.7] ETSI ES 202 396-1: "Speech and multimedia Transmission Quality (STQ); Speech quality
performance in the presence of background noise; Part 1: Background noise simulation technique
and background noise database".
[i.8] ETSI EG 202 396-2: "Speech Processing, Transmission and Quality Aspects (STQ); Speech
quality performance in the presence of background noise; Part 2: Background noise transmission -
Network simulation - Subjective test database and results".
[i.9] ETSI EG 202 396-3: "Speech and multimedia Transmission Quality (STQ); Speech Quality
performance in the presence of background noise; Part 3: Background noise transmission -
Objective test methods".
[i.10] ETSI TS 103 106: "Speech and multimedia Transmission Quality (STQ); Speech quality
performance in the presence of background noise: Background noise transmission for mobile
terminals-objective test methods".
[i.11] ISO 3382-1: "Measurement of room acoustic parameters -- Part 1: Performance spaces".
3 Definition of terms, symbols and abbreviations
3.1 Terms
Void.
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9 ETSI TS 103 224 V1.5.1 (2020-03)
3.2 Symbols
For the purposes of the present document, the following symbols apply:
c Sound velocity
C Matrix of FFT coefficients of Compensation Filters
H Matrix of FFT coefficients of Impulse Responses
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
DUT Device Under Test
EEP Ear canal Entrance Point
FFT Fast Fourier Transform
HATS Head And Torso Simulator
IR Impulse Response
MLS Maximum Length Sequence
MOS Mean Opinion Score
SNR Signal to Noise Ratio
SPL Sound Pressure Level
4 Methods for realistic sound reproduction
For reproduction of real world sound fields there exists a variety of different methods, two of them are wave field
synthesis [i.1] and Ambisonics [i.2]. Both methods, however, require a large number of microphones and loudspeakers
to achieve a sound field reproduction which is sufficiently good for testing purposes. The Wave-Field synthesis setup is
that complex and expensive that it can be neglected for laboratory purposes. Ambisonics, for example, has to be
performed using 43 microphones and 43 loudspeakers to reach a good sound field reproduction up to 2 kHz in a sweet
spot with radius 15 cm (using the rule of thumb in [i.3]). It furthermore cannot consider individual room characteristics
or insufficiencies, but is only designed for rooms offering pure free field conditions. If, e.g. for testing purposes a
HATS is positioned in the artificial noise field, the reproduction quality is reduced by an unknown amount. In summary,
the Ambisonics approach is due to its design not feasible for the intended testing scenario.
The present document introduces an alternative least mean squares method [i.4], which requires eight recording
channels and eight loudspeakers in order to achieve reasonably good reproduction results. The method is based on eight
sweet spots at important testing positions e.g. near the HATS, mainly at the microphone positions of modern phones.
A reasonable reproduction of the recorded sound field at the corresponding eight points in the reproduction situation
also yields good reproduction accuracy in between these points. This well-known property of sound fields is limited to
an upper cut-off frequency which depends on the distances between the recording microphones (see clause 5.1.1).
In clause 5, the recording technique required for this new method is described, while the setup allowing the
reproduction in laboratories and the different steps of the equalization procedure are introduced in clause 6.
5 Recording arrangement
5.0 General
The sound field recording technique (Multi-point sound field recording technique) is based on optimization of the sound
field reproduction at different points in space. The optimization criterion is based on minimization of the reproduction
error at each microphone position. Based on this principle the microphone locations and as a consequence the points in
space for which the sound field reproduction is mostly accurate can be chosen in a wide range. The advantage of the
method is that these locations can be adapted to the type of device which is to be tested. E.g. if the Device Under Test
(DUT) incorporates a microphone array of the Multi-point sound field recording microphones can be positioned in the
area of the microphones of the DUT. If a hands-free device is to be tested the Multi-point sound field recording
microphones are positioned in the area of the hands-free device.
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10 ETSI TS 103 224 V1.5.1 (2020-03)
The setup described in detail in clause 5 is optimized for the testing of handset or headset terminals using HATS
according to Recommendation ITU-T P.58 [i.6] and for hands-free testing. The procedure described here can be
followed in the same way for other microphone setups.
In this clause the setups for the microphone arrangements as used in the present document are described. The
background noise recordings based on these different recording setups are described in clause 8.
5.1 Microphone array setup
5.1.1 Principle limitations
With a perfect sound field reproduction at two closely spaced points, the cut-off frequency up to which the sound field
in between those two points is also correctly reproduced depends on their distance. This upper cut-off frequency can be
estimated as:

=
2
 (1)
where d is the maximum distance between two microphones and c is the sound velocity.
max
EXAMPLE: For the eight microphones in Figure 1, f is dependent on the distance of the microphone pair
lim
considered and is about 1,7 kHz in the region of sparsely spaced microphones and approximately
3 kHz in the region of densely spaced microphones. Note, that at the microphone positions itself
the reproduction quality is optimal across the whole frequency range. In between of these positions
the accurate spatial reproduction can only be guaranteed up to f .
lim
5.1.2 Microphone calibration
In order to yield a good sound field reproduction at the defined positions, the microphone array for recording of the real
sound field and the microphone array for equalization and calibration of the reproduction setup have to match. In detail,
the frequency/phase response and the directional sensitivity of the corresponding microphones of the two arrays has to
be identical. As a consequence, each microphone has to be calibrated individually with regard to frequency response,
phase response and level.
The supplier of such devices should provide information regarding the sensitivity of the individual microphones
constituting the microphone array for verification purposes. The calibration data provided need to be suitable to ensure
a proper phase calibration up to at least 3 kHz, a proper frequency response calibration in the frequency range between
th
50 Hz and at least 3 kHz with an accuracy of < 0,5 dB in 1/12 octave, between 3 kHz and 10 kHz with an accuracy of
rd rd
< 0,5 dB in 1/3 octave, between 10 kHz and 20 kHz with an accuracy of < 3 dB in 1/3 octave and a proper level
calibration (at 250 Hz or 1 kHz) with an accuracy of < 0,1 dB.
5.2 Microphone array setup for handset-type and headset
terminals
Figure 1 shows the configuration of microphones located around an artificial head. The locations of the microphones
define the sweet spots where the reproduction of the recorded signals is optimal for all frequencies. In consequence the
majority of these points are at relevant po
...