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					Applied Psychoacoustics
Lecture: Binaural Hearing




              Jonas Braasch
               Jens Blauert
     4D                      2x 1D                 4D ?
                            Eardrum

                left ear
  3D acoustic                                    3D auditory
    scene                                          scene
                right ear

signal s(t):    Coding        sl(t)   Decoding
distance                      sr(t)
azimuth
elevation
   Types of Binaural Models

• Localization Models
• Detection Models
• Sound-Source Separation Models

• Pink Models
• Black-Box Models
   Types of Binaural Models

• Localization Models
• Detection Models
• Sound-Source Separation Models

• Pink Models
• Black-Box Models
          Tasks to solve

1 What cues are available to localize a
  sound source?
2 How can we extract those cues in a
  Binaural Computational Model?
3 How can we calculate the position of the
  sound source from the extracted
  binaural cues ?
1. What cues are available to localize a sound source?
  Models regarding one sound source
1. What cues are available to localize a sound source?
  Models regarding one sound source
              Head-Related Coordinate System




                    a
   Those cues are available:


• Interaural cues
  – Interaural Time Differences (ITD‘s)
  – Interaural Level Differences (ILD‘s)
• Monaural cues
  – Spectral Cues
   Those cues are available:


• Interaural cues
  – Interaural Time Differences (ITD‘s)
  – Interaural Level Differences (ILD‘s)
• Monaural cues
  – Spectral Cues                    Rayleigh‘s
                                     Duplex Theorie
HRIR
HRIR


       HRTFL   HRTFR
                 Lateralization

   Sideward deviation=1-D task




    Interaural
    axis




Lateralization=intra cranial
Localization =extra cranial      figure from Jens Blauert
How to generate ITDs and ILDs

    ILDs                 ITDs




           attenuators          delay lines




                          figure from Jens Blauert
                        Lateralization Blur for ILDs
  Lateralization blur




                                    Gaussian tones

                                              sinusoid
                                              s




                                      Frequenc
                                      y
Lateralization blur=Lateralization experiments
                                         figure from Jens Blauert
Minimal audible angle=Localization experiments
                      ILD induced Lateralization

                                            left    right
                                       stronger     stronge
                                                    r
perceived sideways deviation


                               right
                               left




                                                   600-Hz
                                                   sinusoid
                                                   (Sayers, 1964)
                                                   broadband noise



                               inter aural level
                                                                     figure from
                               differences
                                                                     Jens Blauert
         Lateralization Blur for ITDs
               frequency band                         Gaussian
               wide                                   tones:
                    carrier
               Gaussian tones
     carrier
envelope or




                   envelope                           Gaussian
                   total signal                       enveloped
                   pure tones
                                                      sinusoids
                                                      of critical band
                                                      width




                                  fcarrier


                                             figure from Jens Blauert
Envelope vs. Carrier Signals
                               ITD induced Lateralization
                                          left earlier    right earlier
perceived sideways deviation


                                right
                                left




                                        inter aural phase differences


                                                                          figure from Jens Blauert
        Localization Curves




                                     auditory event
auditory event




                                     direction of
direction of




                                     φ→
φ→




                 level difference                     time difference
                     (left louder)                       (left earlier)




                                     figure from Jens Blauert
          Tasks to solve

1 What cues are available to localize a
  sound source?
2 How can we extract those cues in a
  Binaural Computational Model?
3 How can we calculate the position of the
  sound source from the extracted
  binaural cues ?
 How can we extract those cues in a
  Binaural Computational Model?
• Extracting ITD‘S
  – Jeffress Model
  – Cross-Correlation Models
• Extracting ILD‘s
  – Excitation-Inhibition cells
The Jeffress Model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +       Jeffress
L   t       t       t       t       t       t   model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +       Jeffress
L   t       t       t       t       t       t   model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +       Jeffress
L   t       t       t       t       t       t   model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +       Jeffress
L   t       t       t       t       t       t   model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +
                                                Jeffress
L   t       t       t       t       t       t   model (1948)
    Estimation of ITDs




    t       t       t       t       t       t
                                                R
        +       +       +       +       +       Jeffress
L   t       t       t       t       t       t   model (1948)
        Estimation of ITDs




        t       t       t       t       t       t
                                                    R
            +       +       +       +       +       Jeffress
    L   t       t       t       t       t       t   model (1948)
Y
                                Interaural cross correlation

                                                           t
                                         to: HRTFr

 Sound sources


   Outer ear




                                 HRTFl
                                                        HRTFl


                                              +



                                ith
                                                                        1st




                         nth
                                                  2nd
                                                                                 band:
                                                                              frequency




Bandpass filter bank

    Haircell




                         H
                                              H
                                                                     H



    Behavior



                         x
                                              x
                                                                     x




Cross-correlation


                    RM
                                         RM
                                                                RM




   Remapping
                                                                              y1 y2 yn




    Haircell
                         H
                                              H
                                                                     H




    Behavior
                                                                                         Decision device




Bandpass filter bank
                                                                                                           Model Structure




                                              +
                                              HR




   Outer ear
                                                             HRTF




                                 HRTFr
                                                        r
                                                        Halfwave
                                                        rectification



                               filter




                                from: sound sources
                                              LP
                               Lowpass
Cross-Correlation Models

                     t1
YY (t)= 1/(t1-t0)   S Y (t)Y (t+t)
                           l   r
                    t=t0




                                   Cherry (1959)
   Cross-Correlation Models
     Similarity to Jeffress‘ Coincidence Model:
                         t1
   YY (t)= 1/(t1-t0)    S Y (t)Y (t+t)
                               l     r
                        t=t0




tk tk+1 tk+2 tk+3 tk+4 tk+5 tk+6 tk+7 tk+8
                                                Fletcher (1940)
Bandpass Filterbank                             Patterson et al. (1995)

                       10


                        0


                       -10
Filter Response [dB]




                       -20


                       -30


                       -40


                       -50


                       -60 2        3                    4
                         10       10                  10
                               Frequency [Hz]
                                        to: HRTFr

 Sound sources


   Outer ear




                                HRTFl
                                                       HRTFl


                                             +



                               ith
                                                                    1st




                         nth
                                                 2nd
                                                                             band:
                                                                          frequency




Bandpass filter bank

    Haircell



                         H
                                             H
                                                                    H



    Behavior


                         x
                                             x
                                                                    x




Cross-correlation


                    RM
                                        RM
                                                               RM




   Remapping
                                                                                                       Model Structure

                                                                          y1 y2 yn




    Haircell
                         H
                                             H
                                                                    H




    Behavior
                                                                                     Decision device




Bandpass filter bank
                                             +




   Outer ear
                                HRTFr
                                                       HRTFr




                               from: sound sources
                                                                                                          Blauert und Cobben (1978)
                 1.0
                                                                      Testsound 1
                 0.5                                                  ff=500 Hz
rel. amplitude




                 0.0

                                                                       Time
                 -0.5



                 -1.0

                    0   0.02   0.04              0.06   0.08   0.1
                                      time [s]
                   0

                                                                      Frequency
dB




                 -50

           -100
              0.0       2.5    5.0         7.5          10.0   12.5
                               Frequency [kHz]
Cross-correlation
Band 7 (527 Hz)
Cross-correlation
Band 11 (3809 Hz)
                 Uncertainty in High Frequencies


                                                          L
rel. amplitude




                                                          R

           0           0.5       1       1.5          2
                             time [ms]            -3
                                               x 10
                 Uncertainty in High Frequencies
                     ?     ?   ?


                                                                L
rel. amplitude




                                                                R

           0             0.5           1       1.5          2
                                   time [ms]            -3
                                                     x 10
                 1.0
                                                                     Testsound 1
                                                                     ff=500 Hz
                 0.5                                                 modulated
rel. amplitude




                 0.0



                 -0.5



                 -1.0

                    0   0.02   0.04              0.06   0.08   0.1
                                      time [s]
                                        to: HRTFr

 Sound sources


   Outer ear




                                HRTFl
                                                       HRTFl


                                             +



                               ith
                                                                    1st




                         nth
                                                 2nd
                                                                             band:
                                                                          frequency




Bandpass filter bank

    Haircell




                         H
                                             H
                                                                    H



    Behavior



                         x
                                             x
                                                                    x




Cross-correlation


                    RM
                                        RM
                                                               RM




   Remapping
                                                                          y1 y2 yn




    Haircell
                         H
                                             H
                                                                    H




    Behavior
                                                                                     Decision device




Bandpass filter bank
                                                                                                       Model Structure




                                             +




   Outer ear
                                HRTFr
                                                       HRTFr




                               from: sound sources
                                         to: HRTFr

 Sound sources


   Outer ear




                                 HRTFl
                                                        HRTFl


                                              +



                                ith
                                                                        1st




                         nth
                                                  2nd
                                                                                 band:
                                                                              frequency




Bandpass filter bank

    Haircell




                         H
                                              H
                                                                     H



    Behavior



                         x
                                              x
                                                                     x




Cross-correlation


                    RM
                                         RM
                                                                RM




   Remapping
                                                                              y1 y2 yn




    Haircell
                         H
                                              H
                                                                     H




    Behavior
                                                                                         Decision device




Bandpass filter bank
                                                                                                           Model Structure




                                              +
                                              HR




   Outer ear
                                                             HRTF




                                 HRTFr
                                                        r
                                                        Halfwave
                                                        rectification



                               filter




                                from: sound sources
                                              LP
                               Lowpass
Cross-correlation
Band 21 (3809 Hz)
Estimating ILDs using EI-cells

 E(j)=exp((10j/40 Pl-10-j/40 Pr)2)




Reed and Blum (1990)      J=ILD
Breebaart et al. (2001)
    Estimating ILDs using EI-cells

     E(j)=exp((10j/40 Pl-10-j/40 Pr)2)
                                       R
     J1 J2 J3 J4 J4 J5 J6
L

    Reed and Blum (1990)      J=ILD
    Breebaart et al. (2001)
EI model
Band 25 (6281 Hz)
          Tasks to solve

1 What cues are available to localize a
  sound source?
2 How can we extract those cues in a
  Binaural Computational Model?
3 How can we calculate the position of the
  sound source from the extracted
  binaural cues ?
3. How can we calculate the position of the sound
    source from the extracted binaural cues ?
3. How can we calculate the position of the sound
    source from the extracted binaural cues ?
                                                                                                             Decision device
                                         frequency
                                            band:                                                                      y1 y2 yn

                                              1st                             H           x                                       H
                                                                                                            RM




                                                                                                                                                                                 from: sound sources
                             HRTFl                                                                                                                                  HRTFr

                                                                              H           x                                       H
 to: HRTFr




                                              2nd
                                          +                                                                                                                     +
                                                                                                            RM
                             HRTFl                                                                                                                                  HRTFr
                                              ith


                                              nth                             H           x                                       H
                                                                                                            RM
                                                     Bandpass filter bank




                                                                                                                                         Bandpass filter bank
                                                                                       Cross-correlation
             Sound sources




                                                                                                           Remapping
                             Outer ear




                                                                                                                                                                     Outer ear
                                                                            Behavior




                                                                                                                              Behavior
                                                                            Haircell




                                                                                                                              Haircell
3. How can we calculate the position of the sound
    source from the extracted binaural cues ?
                                                                                                             Decision device
                                         frequency
                                            band:                                                                      y1 y2 yn

                                              1st                             H           x                                       H
                                                                                                            RM




                                                                                                                                                                                 from: sound sources
                             HRTFl                                                                                                                                  HRTFr

                                                                              H           x                                       H
 to: HRTFr




                                              2nd
                                          +                                                                                                                     +
                                                                                                            RM
                             HRTFl                                                                                                                                  HRTFr
                                              ith


                                              nth                             H           x                                       H
                                                                                                            RM
                                                     Bandpass filter bank




                                                                                                                                         Bandpass filter bank
                                                                                       Cross-correlation
             Sound sources




                                                                                                           Remapping
                             Outer ear




                                                                                                                                                                     Outer ear
                                                                            Behavior




                                                                                                                              Behavior
                                                                            Haircell




                                                                                                                              Haircell
Remapping
  0°   30°



        Model based on
        EI-cells

90°
     4D                      2x 1D                  4D
                            Eardrum

                left ear
                                        ITDs
  3D acoustic                           ILDs      3D auditory
    scene                             monaural      scene
                right ear
                                        cues
signal s(t):    Coding        sl(t)    Decoding
distance                      sr(t)
azimuth
elevation
Head-related Coordinate System

 frontal plane      median
                    plane


backward
φ=180°
=0°
                             forward
horizontal                   φ=0°
                             =0°
plane




                    figure from Jens Blauert
Head-related transfer
     functions




       Frequency [Hz]
Head-related transfer
     functions




  left
  right



          Frequency [Hz]
                                   Head-related transfer
Interaural time differences [ms]        functions




                                          Frequency [Hz]
                                    Head-related transfer
Interaural level differences [dB]        functions




                                           Frequency [Hz]
Localization in the Median Plane
                        directional
                            bands




                                 judgement
                                       rel.
Signal: 1/3 oct. Band noise
                   boosted bands
                                          level
                                   differences




   Monaural Cues                                  Blauert 1969/70
Localization of a single sound source
Types of accompaning sound sources

  • Non-coherent sound sources
    – independent sound sources (e.g. street
      noise, concurrent speakers, accompaning
      musical instruments)
  • Coherent sound sources
    – wall reflections
    – electronically processed sound sources (e.g.,
      loudspeaker arrays)
Part I
         Localization of a single sound source

Part II
      Localization in the presence of a non-
      coherent sound source

Part III
      Localization in the presence of coherent
      sound sources
    Time Course




           target

        distracter
200ms       200ms    100ms
                  Methods


• Virtual auditory sound sources
• Individual HRTF
• 11 listeners, 10 repetitions
• Test sound and distracter:
  – noise (200 - 14 kHz)
  – T/D-ratio 0 ... - 15 dB
• GELP
                                       Localization Results
                            90
                                         Single source
                                         SNR: 0dB
                            60
perceived left/right [° ]




                            30

                             0

                            -30

                            -60

                            -90
                                  -90 -60 -30     0 30 60          90
                                        presented left/right[° ]
Localization Results




                  Listener 6:
                  anechoic
                  condition
                                        to: HRTFr

 Sound sources


   Outer ear




                                HRTFl
                                                       HRTFl


                                             +



                               ith
                                                                    1st




                         nth
                                                 2nd
                                                                             band:
                                                                          frequency




Bandpass filter bank

   Halfwave
  rectification


                         x
                                             x
                                                                    x




Cross-correlation

                    RM
                                        RM
                                                               RM




   Remapping
                                                                          y1 y2 yn




   Halfwave
  rectification
                                                                                     Decision device




Bandpass filter bank
                                                                                                       Localization model



                                             +




   Outer ear
                                HRTFr
                                                       HRTFr




                               from: sound sources
Lateralization shifts at 0 dB T/D-ratio



                                             listeners
                               90
                                            Single source
                                            SNR: 0dB
                               60
   perceived left/right [° ]




                               30

                                0

                               -30

                               -60

                               -90
                                     -90 -60 -30     0 30 60          90
                                           presented left/right[° ]


                                                        distracter         distracter
Running interaural   60 dB
cross-correlation

frequency band: 5




   0 dB              -10 dB
                          Localization
                          Experiment




 target        target
distracter   distracter
  Arguments for the cross-correlation
       difference hypothesis

• two noise bursts are perceived as one
  auditory event, if their envelope is
  identical and they overlap in spectrum.
  This can be observed, even if the noise
  burst have different spatial positions and
  if they are uncorrelated.
• the auditory event of the target depends
  strongly on the exposure time of the
  masker before the target onset.
• existing models fail at very low SNRs.
The interaural cross-correlation difference function

                 YT
                                        YT
          YD‘    YD
     200ms      200ms   100ms

step 1:
                        YA             YT
YT = YA- YD
                                               YT
                                  YD
step 2:
                        YA             YT
YD‘ Y D
                                 YD‘           YT‘
YT‘  YA- YD‘
                                time    time
Total signal            Target




                                           sig: 30°
                                           dis: 0°
Distracter     Total signal - Distracter
Lateralisation shifts
            Meunier et al. (1996)




                       Simulation using
                       subtraction factor g:
                       YT = YA-g(t)YD‘
                       with   a) g(0)=0;
                              b) g(x0)=1;
Including a detection algorithm




                    SNR=-15 dB
               Conclusion

• The model is able to simulate localization and
  detection of broadband noise in broadband
  noise
• It allows localization at very low T/D-ratios
• The model explains a number of
  psychoacoustical phenomena (e.g. shifts of
  auditory events, clustering of responses)
• It can be extended to more than two sound
  sources
Part I
         Localization of a single sound source

Part II
      Localization in the presence of a non-
           coherent sound source

Part III
      Localization in the presence of
      coherent sound sources
The precedence effect




                   (Blauert, 1983)
                      Time course


                                                left
                                              channel
                                               right
ITD 1         ITD 2                           channel
                                    time
        ISI
                                       lead
                                       lag
                 Methods


• Stimulus presentation via headphones
• Lead and lag pair:
  – Bandpass filtered noise (500 Hz cf)
  – 100 Hz, 400 Hz or 800 Hz frequency range
  – Lead: 300 ms ITD, lag: —300 ms and vice
    versa
  – ISI 0, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.5 ms
• 6 listeners
• Acoustic pointer
Psychoacoustial results
 Revised precedence effect
curve for narrow-band signals
   lead




           delay Δt of the lag speaker

     lag


                        Blauert & Braasch 2004
     ISI [ms]




ILD analysis
        Specialized Models
• Combining Several Cues
  – Centrality and Straightness (Stern et al., 1988)
  – HRTF-adjustment (Gaik-Lindemann, 1990)
  – Neuronal Networks (z.B. Janko et al. 1996)
• Localizing more than one sound source
  – Contralateral Inhibition (Lindemann, 1986)
  – Bayes Classification (Nix, Hohmann, 1999)
  – Cross-Correlation Difference (Braasch, 2001)
Importance of Head movements




               Jonghees and van der Veer 1958
                                                                   Median values
azimuth angle φ of auditory event




                                                                   and
                                                                   variations
                                                                   between
                                                                   listeners




                                    level differences between both loudspeaker
                                                                        signals
                                                                    figure from Jens Blauert

				
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