Abstract
A head-related transfer function (HRTF) describes an acoustic transfer function between a point sound source in the free-field and a defined position in the listener’s ear canal, and plays an essential role in creating immersive virtual acoustic environments (VAEs) reproduced over headphones or loudspeakers. HRTFs are highly individual, and depend on directions and distances (near-field HRTFs). However, the measurement of high-density HRTF datasets is usually time-consuming, especially for human subjects. Over the years, various novel measurement setups and methods have been proposed for the fast acquisition of individual HRTFs while maintaining high measurement accuracy. This review paper provides an overview of various HRTF measurement systems and some insights into trends in individual HRTF measurements.
Highlights
A head-related transfer function (HRTF) describes an acoustic transfer function between a point sound source in the free-field and a defined position in the listener’s ear canal [1,2]
Since all relevant acoustic cues to localize real sound sources are contained in HRTFs, i.e., interaural level differences (ILDs), interaural time differences (ITDs), and monaural spectral cues [3], HRTFs are commonly applied to synthesize virtual sound images reproduced over headphones or loudspeakers [4,5,6,7]
Where Fourier transformation (FFT)∗ stands for the complex conjugates of FFT. This property can be utilized for the measurement of the acoustic transfer function H ( f ) as shown in Figure 5: aL and bL are separately emitted from the loudspeaker, the recorded signal is transformed in the frequency domain using an N-point FFT, resulting in H ( f ) FFT( aL ) and H ( f ) FFT(bL )
Summary
A head-related transfer function (HRTF) describes an acoustic transfer function between a point sound source in the free-field (without room information) and a defined position in the listener’s ear canal [1,2]. Direction- and distance-dependent individual HRTFs are required to create immersive VAEs. Measuring high-density HRTF datasets for each individual listener is usually a time-consuming task, especially when considering different source–listener distances. There exist various HRTF measurement systems including measurement setups and methods. Enzner et al [36] presented some rapid measurement systems for recording far-field HRTFs and showed trends in acquisition of HRTFs, but focused mainly on continuous measurement methods which they proposed at that time. Depending on the measurement setups used, different fast HRTF measurement methods are reviewed in Sections 4 and 5.
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