HRTF measurement


What is HRTF?

The complex shape of the outer ears leads to many filtering properties that are key to sound localization. Additionally, the head and torso shapes may also lead to spatial cues. These filtering effects are characterized by the head-related transfer function, typically abbreviated HRTF. Often, a generalized one-size-fits-all HRTF is used, as many characteristics of the transfer function are commonly shared amongst all humans. However, individualized HRTFS are more likely to improve spatialization abilities.

What is ITD & IID?

To obtain a natural auditory environment when listening to the sound through headphones, "head-related" signals containing acoustic differences between the two ears provide cues indicating the spatial position of the sound. The differences, known as intramural time difference (ITD) and intramural intensity (or level) difference (IID or ILD), theoretically allow listeners to receive appropriate sound localization and spatial cues, though it is difficult to obtain ideal binaural sound because of the unique characteristics of individual shapes of heads and ears, especially due to pinna. In this experiment, I tried to measure my personal HRTFs by using BACCH binaural microphones.

Hardwares:

Fluke 424D Laser Distance Meter

Tenma 72-947 Sound Level Meter

Strait-Line X3 laser level (azimuth angle measurement)

BACCH Binaural Microphone (48V)

Allen&Heath Mixer

A Genelec 8030B Loudspeaker

Softwares:

ScanIR (MATLAB)

Pro Tools

This experiment was conducted at New York University MARL (22.2 playback system)

Calibration:

1. Measure the distance between the intended speaker and the X spot. (use laser distance meter)

2. Measure the height of microphone (Nov 10, 2017: distance 1.44m, height 1.29m)

3. Calibrate the speaker SPL and the microphone input SPL. (Pro tools -> signal generator (white noise) -> level: -20dB (Nov 10, 2017: 61.2 SPL)

ScanIR(v.1.2.2):

MultichannelIR -> test 3 sec -> play signal 3 times out -> select output channel: (MARL: 7)

make a comment (azimuth, elevation, distance, etc.) for each try before press start button

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