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
Parameters Influencing Speech
Quality
ITU-T
Study Group 12
Sound Quality &
Intelligibility
Naturalness
Speech Individual
Characteristics Listening
Listening & Talking Speech Conversational
Effort Effort
Quality
Environmental Network
Conditions Double Talk Conditions
Expectation
Performance
... Transmission of ...
Background Noise
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The Telephone Conversation:
ITU-T
Study Group 12
End to End Speech Quality
=
Mouth to Ear Speech Quality
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Network Configuration and
Transmission Parameter
ITU-T
Study Group 12
SLR, RLR, TELR ERL Ie, qdu ERL
LSTR, STMR T
ERL Ie, qdu ERL SLR, RLR, TELR
LSTR, STMR
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Interaction Example: DCME and
Echo Canceller
ITU-T DCME Echo Canceller
Study Group 12
s (t) T
2Dr s' (t)
Adaptive /
Filter Echo 4Dr g (t)
g’ (t) T NLP
o Cascaded comfort noise
o Cascaded switching
o Double talk detection
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TG 020
Interaction Example
Terminal/Network
ITU-T Terminal, Network Components
Study Group 12 Mobile
(Room) (Room)
Noise 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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Signal and Noise Transmission in
Handset Telephony
ITU-T 1 Signal (Voice)
2 Noise, Transmission Noise and
Study Group 12 Room Noise
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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Parameters Influencing Speech
Quality During:
ITU-T Conversation
Study Group 12 Talking
linear distortions Listening
• transfer functions
• attenuation linear distortions
• delay • echo
• reverberance .... • reverberancel linear distortions
• delay ...
non linear distortions • transfer functions
• (in) harmonic distortions • attenuation
non linear distortions • reverberancel ....
• clipping • (in)harmonic distortions
• coding ... • clipping non linear distortions
• coding ...
additive noise components • (in)harmonic distortions
(of the echo signal)
• clipping
• system noise
• coding ...
• background noise additive noise components
• echo • system noise
• double talk ... additive noise components
• background noise • system noise
• channel noise...
during single- • background noise
• channel noise...
and double talk (during talking)
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Instrumental Measures for:
ITU-T Intelligibility Speech quality Quality during
Study Group 12 conversation
measurements during single talk:
- frequency responses
Measurements during single-
- loudness ratings
and double-talk:
- switching characteristics
- delay
- distortion measurements
- echo-loss
- measurements of S/N or N
- switching characteristics
measurement signals: - frequency responses
artificial, eventually speech like - loudness ratings
- variation of background noise
measurement during single talk
psychoacoust. motivated measures: measurement signals: speech
P.862 (PESQ) or speech-like
TOSQA
PACE
PAMS ...
measurement signals: speech
or speech-like
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Instrumental Measures
ITU-T “Traditional” Instrumental Measures
Study Group 12 Single Talk Situation: Double Talk Situation:
- Transfer function during double talk
- Transfer function - Loudness Ratings
- Loudness Ratings - Distortion
- Distortion - System-dynamic
- System-dynamic - System-linearity
- System-linearity
- Sensitivity against room noise
- Sensitivity against room noise
- Background noise transmission
- Background noise transm.
- Switching characteristics - 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"
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The Most Important Parameters
for LTI-Terminals (e.g. Handset
ITU-T 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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Typical Single Values
ITU-T SLR
7dB
CLR
0dB
CLR
0dB
RLR
3dB
Study Group 12
TELR a(Echo) a(Echo) TELR
RLR CLR CLR SLR
3dB 0dB 0dB 7dB
OLR = 10dB
planning values:
Fig. 1 G.131
- loudness ratings
- Impairment factors Ie
- delay -> echo cancellation/suppression
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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Double Talk Requirements
ITU-T echo during double talk:
Echo level offset single talk/double talk
16
12
Study Group 12
the effect of echo level 8
dB
increase during double 4
talk on subjects judgement 0
1 1,5 2 2,5 3 3,5 4 4,5
-> MOS
MOS
5
4 level variation between
3
single- and double talk:
2
the effect on subjects
1
0 3 6 9 12 16 20 judgement
-> loudness variation single/double talk
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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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