International Telecommunication Union
The VDA Specification for car handsfree: A step towards improved speech
quality in car type environments.
Balduin, W. (Ford AG); Best, H.(Adam Opel AG); Dietz, M.
(BMW); Eisner, G. (Volkswagen AG); Gierlich, H.W. (HEAD
acoustics GmbH); Hanke, A. (Audi AG); Heise, B. (Porsche AG);
Schaible, M. (DaimlerChrysler AG)
ITU-T Workshop on Standardization in Telecommunication for motor vehicles
ITU Headquarters, 24-25 November 2003
Outline
ITU-T
o Speech Quality: The Relevant Parameters
o Signal Processing in Car Hands-Free Systems
o The VDA Approach:
• Test Setup
• Tests
• Test Signals
o Requirements for further Work and
Standardization
dates
2
ITU-T
Speech Quality from the Users
Perspective
talking
situation
speech
quality
conversational
situation
listening
situation
dates
3
ITU-T
Choice and Design of Subjective
Tests Methods
factors
that cause difficulties
in talking (type B)
factors
that cause difficulties
in listening (type A)
parameter identification
and definition
factors
that cause difficulties
in conversation (type C)
test
design
correlation
to instrumental
laboratory tests
value selection
quality assessment
Comparison
of implementations
dates
quality prediction
under realistic
network conditions
data base
for further tests
4
Parameters Relevant to Quality
ITU-T
o Auditory perceived parameters which
determine the speech quality of hands-free
terminals:
•
•
•
•
•
•
•
dates
Quality of background noise transmission
(Speech) sound quality
Delay and echo
Double talk capability
Switching and echo during double talk
Loudness
(System) noise
5
Hands-Free Signal Processing
ITU-T
Noisereduction
Attenuation
EC
Microphon –
(Array)
NLP
-
NR
Coder
Coder
Modulation
/
Demodulation
H(f )
+
Loudspeaker
EC
CN
Comfort
Noise
Decoder
e.g. GSM - Modul
Decoder
Speech Recognition
dates
6
VDA: The Test Setup
ITU-T
• real car cabin
• installed hands-free
terminal
• System simulator
(GSM, ...)
• Background noise
simulation
• HATS Head and
Torso Simulator
(ITU-T P.58, P.581)
Background
noise
Loudspeaker
equalizer
System
Simulator
(HF)
HFT
Measurement
system
Subwoofer
• VDA Specification or
HQS-HFT
dates
7
ITU-T
dates
The Structure of the VDA
Specification
o Microphone measurements:
• Sensitivity, frequency responses, ambient
noise reduction…
o Hands-free measurements:
• Delay
• Standard parameters (LR, responses, noise,
out of band …)
• Echo related parameters (TCL, vs. time,
spectral…)
• Switching characteristics
• Double talk parameters (attenuation, echo)
• Background noise transmission parameters
8
Microphone Measurements
ITU-T Two test principles:
Measurements
in anechoic
test conditions
• sensitivity
• linearity
• distortions
dates
Measurements
in the car cabin
•
•
•
•
•
•
Sensitivity
linearity
distortions
frequency response
idle noise
ambient noise reduction
9
Hands-free tests
ITU-T
Standardparameters
in the car
Advanced tests in
the car
!
!
!
!
!
!
!
!
dates
Frequency Response
Loudness Ratings
Distortions
Noise
Out of Band signals
Terminal Coupling Loss
!
!
!
!
!
Delay
Background Noise suppression
(DeLSM
Distortions
Echo loss - time variant,
spectral
Double talk performance
Background noise performance
Comfort noise insertion
10
Testsignals:
ITU-T
Speech-like, but adapted to the specific measuerement task:
„Composite Source“ Signals
Artificial Voice
Modulated
Voiced
Sound
dates
11
Testsignals (CSS)
ITU-T
Composite source Signals
Pseudo Noise
Voiced Sound
Pause
Signal description in
ITU-T P.501
dates
12
ITU-T
(Noise)- Measurement with
Activation Test Signal
Test signal
activation CSS
-28.7 dBPa
Test / Analysis
after activation
window length 1s
(smaller if
necessary!)
Analysis
Requirements
GSM < -64 dBm0(P)
(3GPP)
dates
13
Terminal Coupling Loss
ITU-T
Test signal
Activation artificial
voice, -16 dBm0
pseudo noise
sequence -3 dBm0
Analysis
Test / Analysis
Terminal coupling
loss according to
G.122
Requirements
> 40 dB (3GPP)
> 46 dB
recommended (ITU)
> 33 dB at maximum
volume
dates
14
Double Talk Performance
ITU-T
Test signal
Combination of
CS signals
analysis
single talk
Test / Analysis
Level vs. time
Requirements
Type of
classification!
dates
15
ITU-T
Classification based on ITU-T
Rec. P.340
Subjectively
Relevant
Parameter
Type 1
Type 2
Type 3
Full duplex
capability
Partial
duplex
capability
No duplex
capability
(in P.340 and
VDA more
precise)
Objective
Parameter
• aH,SND,DT
• aH, RCV,DT
• Echo
< 3 dB
< 3 dB
≥ 37 dB
12 - 3 dB
10 - 3 dB
36 - 21 dB
> 12 dB
> 10 dB
< 21 dB
attenuation
dates
16
Summary
ITU-T
o Speech quality has to consider the
conversational situation - the listening
situation, the talking situation and double talk
o Objective parameters are combined by
standard parameters as well as specific
parameters determining double talk and
background noise transmission quality
o Specific test signals are suited for the detailed
evaluation of the various parameters
dates
17
ITU-T
To Do:
Requirements for Future Work
o Speech quality in the presence of
o
o
o
o
dates
background noise
Quality of the noise transmission
Dynamic background noise simulation
Speech quality in combination with
varying network quality
Requirements for wideband
conversational speech quality
18