8 Sound Localization

  What's Sound localization ?

      Sound localization

    When we perceive an incoming sound, we can determine not only loudness, pitch and timbre of this sound but also its spatial information such as the direction and distance of its source.
    We call this "Sound Localization". For example, when a person is called from the back, he can perceive this direction.

    If the physical factors of these spatial information are clarified, it is possible to reproduce sound fields realistically.

      How to perceive sounds

      HRTF (Head Related Transfer Function)

      HRTFs (Head-Related Transfer Functions) describe sound transfer characteristics from a source to the listener’s ears. By using these characteristics, we can perceive spatial directions and distances of sounds.

      Fig.HRTF (Head Related Transfer Function)
      HRTFs include the influence of the head and earlobe in a free sound space where there is no reflected wave.

      To HRTF database

        Measurement of HRTFs

          Fig. Speaker array for measuring HRTFs

          HRTFs change according to direction. Furthermore, because HRTFs are influenced by the shape of the head, ears, shoulders and such,they depend on the individual.

          In this laboratory, we are constructing a HRTF corpus measured from over 100 individuals using a speaker array in an anechoic room.
          We then research the relationship between HRTFs and physical sizes.

          Fig. Measured HRTFs
          (comparisons between two subjects)
          Fig. Shape of dummy head

        Cue of Sound Localization

        To perceive if the sound image's position is on the right side or the left side,      

      • Interaural Level Difference      
      • Interaural Time Difference

        in HRTFs play important roles.

        In the median plane that cuts the head in right and left, the difference between the signals of both ears is small. It is said that distinctive peaks and notches in HRTFs are cues to determine the perceived elevation. We investigate directional and individual dependency of these peaks and notches.

      • Fig. Distinctive Peaks and Notches in HRTFs
        (Left : Change in elevation , Right : Change in azimuth)

      Last update: 2017.04.28