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    (English) HRIR with distance control

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    We present an application capable of control the azimuth, elevation, and distance of sound objects in real-time. This 3D spatialization is done by computing the interpolation of a maximum of four HRIRs, depending on the virtual location, in real-time. 

    Discrete impulse response locations. Original and interpolated kernels are denoted by ◦ and ×, respec- tively.
    Discrete impulse response locations. Original and interpolated kernels are denoted by ◦ and ×, respectively.

    BACKGROUND

    • Spatial audio cues are important in virtual environments to increase realism.
    • Convolving sound sources with a binaural head-related impulse response (HRIR) is a popular technique to spatialize them.
    • HRIR measurements are usually captured at a fixed distance, limiting the locations to points on a spherical surface.
    • HRIR datasets including recordings at different distances have become available.

    MATERIAL

    We used the database published in [1], 6344 locations recorded at 65.536 kHz (1024 taps):

    Earprints in the original database
    Elevation ≤ 50º 60º 70º 80º 90º
    Number of earprints 72 36 24 12 1
    Diffuse field average and its inverse used for diffuse field equalization. Note that the original recordings are high-pass filtered with a cutoff frequency of 70 Hz.
    Diffuse field average and its inverse used for diffuse field equalization. Note that the original recordings are high-pass filtered with a cutoff frequency of 70 Hz.

    OFFLINE PROCEDURES

    • Diffuse field equalization for headphone reproduction
    • Regularize grid: spacing 5º in azimuth, 10º in elevation, and 10 cm in distance.
    • Missing locations were linearly interpolated (LERP)
    • Only the right hemisphere HRIRs  were stored in a SQLite database for the real-time application.
    • Create a Pure-data object named hrir˜.

    ONLINE PROCESSES

    • Up to four HRIRs are selected for interpolation.
    • Convolution is computed for every DSP block in Pd (64 samples by default).
    • Constant-power cross-fading with the output of the previous block
    • Fresh interpolations are performed only if the location of the virtual source is changed.
    • Users can specify the number of taps to be used in the interpolation as an argument of the hrir~ object. This number of taps must be a power of two.

    RESULTS

    • Left outlet outputs the convolved signal for the left ear
    • Right outlet outputs the convolved signal for the right ear
    • Adjustable number of taps via HRIR˜ argument

    Linear interpolations used in HRIR˜. Eight circumscribing measurements are regarded as a cube:

    0simplex
    0-simplex
    1simplex
    1-simplex
    2simplex
    2-simplex
    3simplex
    3-simplex

     

     

     

     

     

    REFERENCES

    [1] Tianshu Qu, Zheng Xiao, Mei Gong, Ying Huang, Xiaodong Li, and Xihong Wu. Distance-Dependent Head-Related Transfer Functions Measured With High Spatial Resolution Using a Spark Gap. IEEE Trans. on Audio, Speech & Language Processing, 17(6): 1124–1132, 2009.

    [2] J. Villegas. Locating virtual sound sources at arbitrary distances in real-time binaural reproduction. Virtual Reality, 19(3):201–212, Oct 2015.