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Custom HRTF

RAC uses the 3D-TuneIn Toolkit (3DTI) for HRTF processing. Currently only the .3dti-hrtf file format is supported. If a custom HRTF file is desired, the 3DTI toolkit provides a SOFATo3DTI converter. It can be used as follows: 

HRTF_SOFATo3DTI -i <SOFA file> -o <3dti-hrtf file>
The SOFA file should have the interaural time delay (ITD) removed and left and right ear delays stored in the Delay variable of the SOFA file.

Convert to minimum phase

One approach to remove ITD is to convert the HRTF to minimum phase1. The following MATLAB code can be used: 

function [leftMinPhase, rightMinPhase, leftDelay, rightDelay] = ConvertToMinimumPhase(left, right, fs)
    fc = 3e3;
    threshold = db2mag(-30);

    leftLPF = lowpass(left,fc,fs);
    rightLPF = lowpass(right,fc,fs);

    leftOffset = max(leftLPF) * threshold;
    rightOffset = max(rightLPF) * threshold;

    leftDelay = find(leftLPF > leftOffset, 1, "first") - 1;
    rightDelay = find(rightLPF > rightOffset, 1, "first") - 1;

    [~, leftMinPhase] = rceps(left);
    [~, rightMinPhase] = rceps(right);
end

Select the HRTF in Unity

Once created, the .3dti-hrtf file can be used in the Unity project:

  1. Save the .3dt-hrtf file in the Assets/StreamingAssets folder of your Unity project.
  2. On the RACManager script set the HRTF file to Custom.
  3. Type the name of the .3dt-hrtf file (with the extension) in the text field.
  4. Press play and check the console to ensure the custom HRTF has been loaded successfully.

  1. Andreopoulou A, and Katz B. "Identification of perceptually relevant methods of inter-aural time difference estimation." J. Acoust. Soc. Amer., 142:588–598, 2017 ↩