International Telecommunication Union
ITU-T Study Group 12
Speech Communication from Mouth to
Ear: Voice Quality Aspects in Modern
Telecommunication Networks
Dr.-Ing. H. W. Gierlich
HEAD acoustics
SG12 Workshop Dakar Oct. 2001
ITU-T
Parameters Influencing Speech
Quality
Study Group 12
Sound Quality &
Naturalness
Intelligibility
Speech
Characteristics
Individual
Listening
Listening & Talking
Effort
Environmental
Conditions
...
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Speech
Quality
Double Talk
Performance
Conversational
Effort
Expectation
Transmission of
Background Noise
SG12 Workshop Dakar Oct. 2001
Network
Conditions
...
2
The Telephone Conversation:
ITU-T
Study Group 12
End to End Speech Quality
=
Mouth to Ear Speech Quality
ITU-T
3
SG12 Workshop Dakar Oct. 2001
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Network Configuration and
Transmission Parameter
Study Group 12
SLR, RLR, TELR
LSTR, STMR
ERL
Ie, qdu
ERL
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ERL
Ie, qdu
T
ERL
SG12 Workshop Dakar Oct. 2001
SLR, RLR, TELR
LSTR, STMR
4
ITU-T
Interaction Example: DCME and
Echo Canceller
DCME
Study Group 12
Echo Canceller
T
s (t)
Adaptive
Filter
g’ (t)
T
Echo
2Dr
/
4Dr
s' (t)
g (t)
NLP
o Cascaded comfort noise
o Cascaded switching
o Double talk detection
5
SG12 Workshop Dakar Oct. 2001
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TG
ITU-T
Study Group 12
020
Interaction Example
Terminal/Network
Terminal,
Mobile
Network Components
(Room)
Noise
(Room)
Noise
o Noise and addition of comfort noise
o Cascaded switching
o Speech detection and noise
o Cascaded speech coding & various types of noise
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SG12 Workshop Dakar Oct. 2001
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ITU-T
Signal and Noise Transmission in
Handset Telephony
1 Signal (Voice)
2 Noise, Transmission Noise and
Room Noise
Study Group 12
3 Noise, Sidetone Coupling
4 Noise, Acoustical Sidetone
5 Noise, Structure Borne
6 Noise, Bone Conduction
7 Noise, Coupled to Ear
not Covered by the Handset
4
6
6
2
1
7
3
5
3
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The Hands-Free Situation
ITU-T
Study Group 12
e
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ITU-T
Parameters Influencing Speech
Quality During:
Conversation
Study Group 12
Talking
linear distortions
Listening
• transfer functions
• attenuation
• delay
• reverberance ....
linear distortions
non linear distortions
• (in) harmonic distortions
• clipping
• coding ...
additive noise components
• system noise
• background noise
• echo
• double talk ...
during singleand double talk
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• echo
• reverberancel
• delay ...
non linear distortions
• (in)harmonic distortions
• clipping
• coding ...
(of the echo signal)
additive noise components
• system noise
• background noise
• channel noise...
(during talking)
linear distortions
• transfer functions
• attenuation
• reverberancel ....
non linear distortions
• (in)harmonic distortions
• clipping
• coding ...
additive noise components
• system noise
• background noise
• channel noise...
9
SG12 Workshop Dakar Oct. 2001
Instrumental Measures for:
ITU-T
Study Group 12
Intelligibility Speech quality Quality during
conversation
measurements during single talk:
- frequency responses
- loudness ratings
- switching characteristics
- distortion measurements
- measurements of S/N or N
measurement signals:
artificial, eventually speech like
measurement during single talk
psychoacoust. motivated measures:
P.862 (PESQ)
TOSQA
PACE
PAMS ...
measurement signals: speech
or speech-like
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SG12 Workshop Dakar Oct. 2001
Measurements during singleand double-talk:
- delay
- echo-loss
- switching characteristics
- frequency responses
- loudness ratings
- variation of background noise
measurement signals: speech
or speech-like
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tg_e056
Instrumental Measures
ITU-T
Study Group 12
“Traditional” Instrumental Measures
Single Talk Situation:
Double Talk Situation:
- Transfer function during double talk
- Loudness Ratings
- Distortion
- System-dynamic
- System-linearity
- Transfer function
- Loudness Ratings
- Distortion
- System-dynamic
- System-linearity
- Sensitivity against room noise
- Background noise transm.
- Switching characteristics
- Sensitivity against room noise
- Background noise transmission
- Switching and echo characteristics
- Measurement applied to complete end to end configuration
- Terminals must be included
- Noise conditions (at the subscriber) need to be included
“Listen and Analyze"
01.10.2001
ITU-T
SG12 Workshop Dakar Oct. 2001
11
The Most Important Parameters
for LTI-Terminals (e.g. Handset
Terminals)
Study Group 12
• Frequency response in sending & SLR
• Frequency response in receiving & RLR
• Background noise sensitivity in sending ( SM)
∆
• Background noise sensitivity in receiving (LSTR)
• Echo performance (TCL, ERLt)
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Performance Limits:
ITU-T
Study Group 12
o Echo: G.131(single talk and double talk
o G.168 (echo canceller)
o Loudness Ratings: P.79
o Switching characteristics: P.340
o E-model: G.107, G.108, G.108.1, G.113
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SG12 Workshop Dakar Oct. 2001
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Typical Single Values
ITU-T
SLR
7dB
CLR
0dB
CLR
0dB
RLR
3dB
Study Group 12
TELR a(Echo)
RLR
3dB
a(Echo)
CLR
CLR
0dB
0dB
OLR = 10dB
TELR
SLR
7dB
planning values:
- loudness ratings
- Impairment factors Ie
- delay -> echo cancellation/suppression
Fig. 1 G.131
problems:
• values frequency dependant
• non linear, time variant transmission properties
• proper consideration of codecs, cascading of codecs, echo cancellers..
• interaction of different transmission systems (e.g. PSTN, IP...)
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SG12 Workshop Dakar Oct. 2001
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Double Talk Requirements
ITU-T
Study Group 12
Echo level offset single talk/double talk
16
echo during double talk:
the effect of echo level
increase during double
talk on subjects judgement
12
8
dB
4
0
1
1,5
2
2,5
3
-> MOS
3,5
4
4,5
MOS
5
4
3
2
1
0
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3
6
9
12
16
20
-> loudness variation single/double talk
level variation between
single- and double talk:
the effect on subjects
judgement
SG12 Workshop Dakar Oct. 2001
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Conclusions
ITU-T
Study Group 12
o Typical network conditions and user
conditions have to be taken into account
o Overall quality description not complete
yet for non LTI-systems
o Various quality parameters for single and
double talk situations available in ITU
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