ITU-T Study Group 12

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					                      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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