Speech Quality in eCall Systems
eCall and Voice Quality
–
The forgotten Dimension
ITU-T The Future Networked Car 2014
H. W. Gierlich, F. Kettler
The eCall system architecture in a car
GPS (GLONASS)
receiver
3GPP TS 26.267
MSD
IVS
(minimum set of data)
(in vehicle system)
information source
data modem
Speech Codec
Radio Link
Hands Free
Hands-Free
for eCall
?
Gierlich, Kettler
© HEAD acoustics GmbH
eCall and Voice Quality
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Speech Quality in eCall Systems
Standards for Voice Quality in Car Hands-Free
VDA Specification for car hands-free systems
since 2001 – targeted to narrow-band integrated car hands-free
ITU-T P.1100: Narrowband hands-free communication
in motor vehicles
since 2008 – targeted to integrated, after-market car hands-free & headsets
ITU-T P.1110: Wideband hands-free communication
in motor vehicles
since 2010 – targeted to integrated,
integrated after-market
after market car hands-free
hands free & headsets
ITU-T P.VSSR : Subsystem requirements for
automotive speech services
work ongoing since 2010 – targeted to integrated car hands-free
Gierlich, Kettler
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Parameters Considered in Present Standards
Speech Quality
Sending
Echo
Performance
Double Talk
Performance
Gierlich, Kettler
© HEAD acoustics GmbH
Speech Quality
Receiving
Speech
Quality
Switching
Performance
Background Noise
Performance
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Speech Quality in eCall Systems
What is Different, what is Missing for Emergency Call Systems
Speech
Intelligibility
Sending
Speech
Intelligibility
Receiving
Speech Quality
Sending
Echo
Performance
Double Talk
Speech Quality
Receiving
Speech
Quality
Double Talk
Performance incl.
Performance
Intelligibility in DT
Gierlich, Kettler
Switching
Performance
Background Noise
Performance
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The Acoustical Situation in a Car
Sending –
speech pickup by
the microphone
Receiving –
speech reception by
the passengers
p
g
Coupling between
loudspeaker and
microphone
Background Noise –
pickup by
the microphone
Background Noise –
in addition to
speech in receive
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© HEAD acoustics GmbH
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Speech Quality in eCall Systems
Potential System Constraints for eCall Systems
 Costs – eCall systems should be produced at minimum costs
 Reliabilityy – eCall systems
should be mostly
of the car
y
y independent
p
systems
 Component limitations
 Potential “one box” design with small loudspeaker
 No advanced microphone technology due to cost and space
requirements
 Limitations in system placement
 Need to be integrated into the car design during the design phase
 General acoustical difficulties in a car cabin
Gierlich, Kettler
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The Different Parameters Influencing the Quality of eCall Seech Services
Relevance to eCall speech services
Parameter in present standards
•
•
Delay
Frequency Response
Loudness Ratings
Distortions
System noise
Out of Band signals
Terminal Coupling Loss
Background noise
performance
Echo p
performance
Double talk performance
Switching performance
Comfort noise insertion
•
Probably less important
Should be targeted to intelligibility
Important basic parameter
Probably less important
Less important if below certain limits
Less important if below certain limits
Probably less stringent requirement sufficient
Important information in the background noise
should be preserved
Probably less stringent requirements needed
Important due to less disciplined conversation
Important due to less disciplined conversation
Less relevant
•
Speech Intelligibility
•
Most important, new tests required
•
•
•
•
•
•
•
•
•
•
•
Gierlich, Kettler
© HEAD acoustics GmbH
•
•
•
•
•
•
•
•
•
•
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Speech Quality in eCall Systems
Main Impact on Testing and Requirements for eCall Speech Services
•
Speech Intelligibility
• In sending probably no objective methodology available
• In receiving
ece g tthe
e app
application
cat o o
of e
existing
st g methods
et ods needs
eeds to be studied
stud ed
Frequency response characteristics – masks need to be adapted
Adjust loudness requirements in receiving to eCall situation
Additional loudness rating requirements in sending for different positions in the car
Echo loss requirements need to be revisited
New focus in background noise situations:
• High
Hi h intelligibility
i t lli ibilit with
ith b
background
k
d noise
i
• Preserve “naturalness” & “recognizability” of the background noise
Preserve double talk capability as much as possible with special focus on
intelligibility during double talk
•
•
•
•
•
•
Gierlich, Kettler
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Considerations for Speech Intelligibility Testing in eCall Systems
•
Speech Intelligibility in receiving
• More “classical” situation – similar to speech intelligibility in rooms
• Potential application of existing methods such as
•
•
•
•
SII (speech intelligibility index)
index),
STIPA (speech transmission index for public address systems)
RASTI (rapid speech transmission index)
Speech Intelligibility in sending
• No well performing objective test method available
• Performance evaluation potentially possible using “second order”
parameters such as
•
•
•
Optimized frequency response characteristics,
Evaluation of switching and double talk performance with focus on speech
intelligibility
Consideration of eCall relevant noise types
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© HEAD acoustics GmbH
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Speech Quality in eCall Systems
Potential Improvements: Speech Intelligibility - Example
Improvement of Speech Intelligibility by Adapting Frequency Response Characteristics
Modified response and resulting intelligibility
+ 20%
Original response and resulting intelligibility
*Gierlich: Sprachverständlichkeit beim Fernsprechen, 1988
Gierlich, Kettler
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Background Noises in eCall Senarios
analysis
analysis
dBSPPL(A)
Spectrum avg. FFT Size:4096 Overlap:0,0% Hanning
100
90
80
70
60
50
40
30
20
10
0
p/dB[Pa]
0
-20
Noise Level
left ear 69,3 68,2
right ear
73,8
-40
68,0
59,4
53,5
41,7 40,0
-60
60
36,4 33,9
-80
Car 130 kmh
20
Gierlich, Kettler
© HEAD acoustics GmbH
eCall and Voice Quality
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Full Size Car 130 kmh binaural
VW Touran, H ighway parking, windows closed
VW Touran, H ighway parking, windows open
Highway, Highway, Quiet street, Quiet street, windows open windows closed windows open windows closed
50
100
200
f /H z 1000 2000
5000
-120
10k
20k
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Speech Quality in eCall Systems
Considerations for eCall System Design
 Use/adapt low power designs from
modern mobile phones
 Choose appropriate locations for the
eCall system components (esp
(esp.
loudspeaker & microphone)
 Consider the integration of existing
microphones/loudspeakers in the car
for use in conjunction with the „one
box“ eCall system
 …
Gierlich, Kettler
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Required Actions in Standardization
 Most efficient solution: develop a standard specifically targeted to
emergency call systems
 Base work on existing ITU-T standards P.1100 and P.1110
 Modify existing requirements and adapt testing procedures where needed
 Remove less relevant parameters
 Amend new standard by new parameters and testing procedures where needed
– especially for speech intelligibility
 Potential home for the work:
ITU-T SG12 – Q.4 dealing with „Hands-free communication and user
interfaces in vehicles”
 ETSI TC STQ
 ….use this standard as baseline standard for emergency call systems
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© HEAD acoustics GmbH
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Speech Quality in eCall Systems
Dr.-Ing. H. W. Gierlich
Dipl.-Ing. F. Kettler
info@head-acoustics.de
www.head-acoustics.de
© Copyright HEAD acoustics GmbH
© HEAD acoustics GmbH
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