Specifying High-Quality HandsFree Speech Communications in
Motor Vehicles
H.W. Gierlich, F. Kettler
HEAD acoustics
Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
HQ HFT Speech Communications
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1
Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
HQ HFT Speech Communications
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“The Hands-free Problem…“
High necessary playback
volume via loudspeaker
Use of handset or headset
(“close to ear“)…
HFT
Low playback volume at
loudspeaker (low distance)
High necessary
microphone sensitivity
(high distance (!))
Low microphone
sensitivity (low distance)
• Loudspeaker – Microphone coupling !!
• Instability !!
• High Sensitivity on Backgroung Noise !!
•…
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2
Algorithms
HFT
gain
…at least 46 dB!
EC
ES
NR
AGC/
gain
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“The Hands-free Problem…“
HFT
gain
EC
ES
NR
AGC/
gain
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3
“The Hands-free Problem…“
HFT
gain
Level vs. time Manual(5,0 ms)
Ch.1 - Ch.2
L/dB
0
EC
-10
-20
-30
-40
-50
-60
0.5
0.75
1
1.25
1.5 t/s
2
2.25
2.5
2.75
ES
NR
AGC/
gain
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Double Talk Performance
Attenuation range in sending direction (P.340) - examples
Level vs. time Manual(5,0 ms)
Ch.1 - Ch.2
L/dB
0
Level vs. time Manual(5,0 ms)
Ch.1 - Ch.2
L/dB
0
0.75
1
1.25
Level vs. time Manual(5,0 ms)
t/s
1.75
2
2.25
Ch.1 - Ch.2
Ch.1 - Ch.2
L/dB
0
-10
-10
-20
-20
-20
-30
-30
-30
-40
-40
-40
-50
-50
-60
0.5
Level vs. time Manual(5,0 ms)
-10
0.5
L/dB
0
-50
-60
2.5 2.75
0.75
1
Level vs. time Manual(5,0 ms)
1.25
t/s 1.75
2
2.25
2.5 2.75
Ch.1 - Ch.2
-60
0.5
L/dB
0
0.75
1
1.25
1.5 t/s
Level vs. time Manual(5,0 ms)
2
2.25
Ch.1 - Ch.2
2.5
2.75
L/dB
0
-10
-10
-10
-20
-20
-20
-30
-30
-30
-40
-40
-40
-50
-50
-50
SND(1) - Source
-60
0.5
0.75
1
1.25
t/s
1.75
2
2.25
2.5 2.75
-60
-60
0.25
0.5
0.75
1
1.25 t/s
1.5
1.75
2
HQ HFT Speech Communications
2.25
2.5
0.5
0.75
1
1.25
t/s 1.75
2
2.25
2.5 2.75
8
4
Mobile Hands-free Terminals
HFT in Vehicles
Massive customer complaints !
Speech Sound in Vehicle
VDA Specification
analysis
Speech Sound at Landside
Echo Problems…
ITU-T P.1100
for “built-in“ hands-free
systems
Double Talk Performance
Transmission Aspects in the
Presence of Background
Noise
for aftermarket products in all
target vehicles
for mobile navigation systems
incl. hands-free functionality
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Activities in Standardization
• Summary and Conclusion
HQ HFT Speech Communications
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5
Complex Systems
Mobile
network
Audio
playback
system
Handsfree
telephone
system
Microphone
array signal
processing
GSM
module
?
GSM
mobile
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Complex Systems
Audio
playback
system
Hands-free
Telephone
System
gain EQU
Microphone array
signal processing
gain
gain
EC
NR
GSM
mobile
EC
ES
ES
NR
NR
AGC/
gain
HQ HFT Speech Communications
AGC/
gain
12
6
Sending (Uplink)
Audio
playback
system
Hands-free
Telephone
System
gain EQU
GSM
mobile
gain
gain
EC
EC
ES
NR
cascaded EC’s
cascaded ES CN
cascaded NR
cascaded AGC’s
ES
NR
NR
Microphone array
signal processing
AGC/
gain
AGC/
gain
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Activities in Standardization
• Summary and Conclusion
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7
Microphone Position
Dashboard
right
A-pillar
bottom
A-pillar
top
Mirror
left
Mirror
right
centre
speak.
Dashboard
right
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
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8
Loudspeaker Position and Mounting
Intelligibility outside vehicles …
analysis
analysis
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Test Setup
• Analysis of loudness, …
• Two audio-visual analysis methods:
{ Laser Vibrometer
HFT
•HFT
{
Acoustical Camera (“Visor“)
•Subwoofer
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9
Analysis: Acoustical Camera
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Analysis: Acoustical Camera
(slow)
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10
Different cars
Speech in cars with different speaker systems
Sweep to locate speaker
positions depending on
emitted frequency
(760 Hz - 1800)
Front speaker used, car
well damped, low level
outside
(1400 - 1800 Hz)
Door speaker used
(1000 – 1500 Hz)
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
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11
Car2Car Communication
Generator
and Analyzer
ACQUA
Background
Noise
HFT
HFT
•HFT
AES / EBU
(Digital)
USB
(Digital)
USB
Frontend
Programmable
Equalizer
PEQ IV
Echo ?
AES / EBU
(Digital)
MFE VI
Programmable
Equalizer
PEQ IV
AES / EBU
(Digital)
Programmable
Equalizer
(Analog)
PEQ IV
Subwoofer
•Subwoofer
Radio Tester
Laboratory setup
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Car2Car Communication
simulated car
car under test
Background
Noise
HFT
HFT
•HFT
AES / EBU
(Digital)
Filter
Programmable
Equalizer
PEQ IV
AES / EBU
(Digital)
ERL
Programmable
Equalizer
PEQ IV
+
AES / EBU
(Digital)
Programmable
Equalizer
PEQ IV
Subwoofer
•Subwoofer
Generator &
Analyzer
Laboratory setup
HQ HFT Speech Communications
Listening examples
24
12
Car2Car Communication
U/V
U/V
2.5
2.5
2
2
1.5
1.5
1
1
0.5
19 dB ERL
0
0.5
13 dB ERL
0
-0.5
-0.5
-1
-1
-1.5
-1.5
-2
-2
-2.5
-2.5
2
3
4
t/s
5
6
2
7
3
4
t/s
5
6
7
U/V
2.5
2
1.5
1
0.5
10 dB ERL
0
-0.5
-1
-1.5
-2
-2.5
2
3
4
t/s
5
6
7
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
HQ HFT Speech Communications
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13
“Idea” behind Wideband
/s/
Spectrum avg. FFT Size:512 Overlap:70,0% Hanning
L/dB[Pa]
-20
narrowband
-25
wideband
Quality and intelligibility!
-30
-35
100
-45
90
-50
-55
-60
0
/o/
500
1500
2500
3500
f/Hz 5500
6500
7500
8500
Spectrum avg. FFT Size:512 Overlap:70,0% Hanning
9500
L/dB[Pa]
0
-20
% of logathom intelligibility^
-40
14%
80
70
60
50
40
30
20
10
0
ISDN
-40
PCM 16 bit
AMR-WB 12.65
kbit/s
Codec
-60
-80
-100
0 500 1000
2000
3000
4000
f/Hz
6000
7000
8000
9000
10k
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ITU-T P.505 “HFT Quality Pie“
Each “slide“ represents
one parameter
Size of each slice
correlates to quality
analysis
analysis
Minimum requirement
(red circle) represents
required / recommended
numbers
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14
ITU-T P.505 “Quality Pie“
Some typical results …
analysis
analysis
1
2
3
4
5
6
7
8
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Overview
• Introduction
• Speech over Hands-free Telephones
• System Complexity
• Microphone Position
• Loudspeaker Position
• Car2Car Communication
• …towards Wideband
• Summary and Conclusion
HQ HFT Speech Communications
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15
Summary and Conclusion
• Optimum car hands-free solution requires the
involvement of the audio engineers in the
construction phase of a car
• Positioning of microphones and loudspeakers in
cars is of critical importance for the overall
quality of the system
• Signal processing needs to be optimized for
each car individually in order to get the best
possible solution
• Cascaded signal processing should be avoided
or at least considered and optimized
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Test Setup
HEAD acoustics Driving
simulator (for stand-alone solutions /
Mobiles Sound Playback System
aftermarket products)
(can be installed in any vehicle)
Test System
analysis
analysis
Generator
and Analyzer
ACQUA
ACQUA
Background
Noise
HFT
AES / EBU
(Digital)
USB
(Digital)
USB
Frontend
Programmable
Equalizer
PEQ IV
AES / EBU
(Digital)
MFE VI
Programmable
Equalizer
PEQ IV
AES / EBU
(Digital)
Programmable
Equalizer
(Analog)
PEQ IV
Subwoofer
Radio Tester
HQ HFT Speech Communications
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16