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1
Content available Continuous Head-related Transfer Function Representation Based on Hyperspherical Harmonics
Szwajcowski Adam
Archives of Acoustics
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2023
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Vol. 48, No. 1
127--139
EN
Expressing head-related transfer functions (HRTFs) in the spherical harmonic (SH) domain has been thoroughly studied as a method of obtaining continuity over space. However, HRTFs are functions not only of direction but also of frequency. This paper presents an extension of the SH-based method, utilizing hyperspherical harmonics (HSHs) to obtain an HRTF representation that is continuous over both space and frequency. The application of the HSH approximation results in a relatively small set of coefficients which can be decoded into HRTF values at any direction and frequency. The paper discusses results obtained by applying the method to magnitude spectra extracted from exemplary HRTF measurements. The HRTF representations based on SHs and HSHs exhibit similar reproduction accuracy, with the latter one featuring continuity over both space and frequency and requiring much lower number of coefficients. The developed HSH-based continuous functional model can serve multiple purposes, such as interpolation, compression or parametrization for machine-learning applications.
2
Content available Research of acoustical impedance of human skin
Plaskota Przemysław
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019143
EN
This paper presents the methodology of measuring acoustic impedance of human skin and discusses the results of the tests. Measurement of the acoustic impedance of human skin is a complex issue. The most difficult thing is related to the nature of the object of research. Cooperation of volunteer participating in the experiment is crucial in collecting accurate data. Appropriate measuring conditions must be provided because of the length of time required to conduct measurement. The Kundt tube method has been used as a research technique applied for evaluation of the material impedance. It was assumed that the results would differ with regard to different points chosen for measurement, located on the body of volunteer as well as with regard to the features of the skin structure of the volunteers participating in this experiment. Results have revealed that for different people similar parameters have been obtained. Moreover, results are alike for various measured points localized on person’s body.
3
Content available Multimodal Perceptual Training for Improving Spatial Auditory Performance in Blind and Sighted Listeners
Bǎlan O., Moldoveanu A., Moldoveanu F.
Archives of Acoustics
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2015
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Vol. 40, No. 4
491--502
EN
The use of individualised Head Related Transfer Functions (HRTF) is a fundamental prerequisite for obtaining an accurate rendering of 3D spatialised sounds in virtual auditory environments. The HRTFs are transfer functions that define the acoustical basis of auditory perception of a sound source in space and are frequently used in virtual auditory displays to simulate free-field listening conditions. However, they depend on the anatomical characteristics of the human body and significantly vary among individuals, so that the use of the same dataset of HRTFs for all the users of a designed system will not offer the same level of auditory performance. This paper presents an alternative approach to the use on non-individualised HRTFs that is based on a procedural learning, training, and adaptation to altered auditory cues.We tested the sound localisation performance of nine sighted and visually impaired people, before and after a series of perceptual (auditory, visual, and haptic) feedback based training sessions. The results demonstrated that our subjects significantly improved their spatial hearing under altered listening conditions (such as the presentation of 3D binaural sounds synthesised from non-individualized HRTFs), the improvement being reflected into a higher localisation accuracy and a lower rate of front-back confusion errors.
4
Content available Magnitude Modelling of HRTF Using Principal Component Analysis Applied to Complex Values
Ramos O. A., Tommasini F. C.
Archives of Acoustics
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2014
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Vol. 39, No. 4
477--482
EN
Principal components analysis (PCA) is frequently used for modelling the magnitude of the head- related transfer functions (HRTFs). Assuming that the HRTFs are minimum phase systems, the phase is obtained from the Hilbert transform of the log-magnitude. In recent years, the PCA applied to HRTFs is also used to model individual HRTFs relating the PCA weights with anthropometric measurements of the head, torso and pinnae. The HRTF log-magnitude is the most used format of input data to the PCA, but it has been shown that if the input data is HRTF linear magnitude, the cumulative variance converges faster, and the mean square error (MSE) is smaller. This study demonstrates that PCA applied directly on HRTF complex values is even better than the two formats mentioned above, that is, the MSE is the smallest and the cumulative variance converges faster after the 8th principal component. Different objective experiments around all the median plane put in evidence the differences which, although small, seem to be perceptually detectable. To elucidate this point, psychoacoustic discrimination tests are done between measured and reconstructed HRTFs from the three types of input data mentioned, in the median plane between −45◦ and +90◦.
5
Content available HRTF Adjustments with Audio Quality Assessments
Yao S. N., Chen L. J.
Archives of Acoustics
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2013
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Vol. 38, No. 1
55--62
EN
There are an increasing number of binaural systems embedded with head-related transfer functions (HRTFs), so listeners can experience virtual environments via conventional stereo loudspeakers or head- phones. As HRTFs vary from person to person, it is difficult to select appropriated HRTFs from already existing databases for users. Once the HRTFs in a binaural audio device hardly match the real ones of the users, poor localization happens especially on the cone of confusion. The most accurate way to obtain personalized HRTFs might be doing practical measurements. It is, however, expensive and time consuming. Modifying non-individualized HRTFs may be an effort-saving way, though the modifications are always accompanied by undesired audio distortion. This paper proposes a flexible HRTF adjustment system for users to define their own HRTFs. Also, the system can keep sounds from suffering intolerable distortion based on an objective measurement tool for evaluating the quality of processed audio.
6
Dependence of the head-related transfer function on pinna flare angle
Plaskota P., Dobrucki A. B.
Elektronika : konstrukcje, technologie, zastosowania
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2009
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Vol. 50, nr 3
19-21
EN
Head Related Transfer-Function (HRTF) describes the modification of the spectrum of acoustic wave arriving to the ear. The HRTF influences sound source localization by auditory system. It has been proved that individual properties strongly influence HRTF. Application of HRTF which is different for each individual decreases the ability of sound source localization by the listener during headphones sound projection. The aim of the paper is the study of influence of pinna flare angle on the HRTF shape.
PL
Funkcja Transmitancji Odniesiona dp Głowy (HRTF) opisuje modyfikację widma fali akustycznej docierającej do ucha. HRTF wpływa na lokalizację źródła dżwięku przez system słuchowy. Zostało udowodnione, że cechy osobnicze silnie wpływają, na HRTF. Zastosowanie HRTF, które jest różne dla każdego słuchacza powoduje pogorszenie zdolności lokalizacji źródła dźwięku podczas odsłuchu przez słuchawki. Celem pracy jest zbadanie wpływu kąta odchylenia małżowiny usznej na przebieg HRTF.
7
Content available remote Conversion of stereo recording to 5.1 format using head-related transfer functions
Hen P., Kin M. J., Plaskota P.
Archives of Acoustics
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2008
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Vol. 33, No. 1
7-10
EN
The paper presents the conversion of stereo recordings into multi-channel format 5.1 by means of the HRTF filtering. An algorithm of additional channels preparation (a central one and two surround ones) using various filters created on the base of HRTF was tested. The filter bank was prepared on the basis of impulse responses given by users. The algorithm uses the impulse response convolution of the filter with a processed signal. The convolution is realized in frequency domain, i.e. Fourier transforms of the processed signals are multiplied. Recordings created in such way were tested for the features of sound color distortion and spaciousness of the audio-scene in frontal plane.
8
Content available remote Automatic measuring system for head-related transfer function measurement
Plaskota P.
Archives of Acoustics
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2008
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Vol. 33, No. 1
19-25
EN
In this paper the Head Related Transfer Function (HRTF) Automatic Measurement Equipment is presented. The system allows to measure HRTF with high spatial resolution within a considerably short time. The system employs many switched sound sources and a rotary chair. HRTF describes a transfer function of the human head and pinna and is unique for each human. Individual measurement of HRTF is necessary for applications where precise simulation of sound source localization is essential. An accurate determination of HRTF requires the position of sound source to be changed in the space surrounding test participants. It necessitates hundreds of measurements with high spatial resolution. The procedure becomes very time consuming and tiring for the participants.
9
Content available Spatial audio reproduction by headphones using binaural room impulse responses measured individually by the listener
Mickiewicz W., Sawicki J.
Pomiary Automatyka Kontrola
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2007
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R. 53, nr 6
30-33
EN
Listening via headphones in opposition to a loudspeaker reproduction introduces changes in the perception of acoustic atmosphere and spaciousness (internalisation effect). This can be changed using the Head Related Transfer Function (HRTF) technology. In the paper there is presented an idea of the headphones processor which uses an individualized Binaural Room Impulse Response (BRIR) measured for a given listener and for a given acoustical environment. There is investigated the influence on the performance of the individualized headphones processor of acoustical properties of the room, length of the BRIR and electroacoustical chain quality. The main goal of this research was to evaluate the minimum requirements, which have to be fulfilled by the processing algorithm to obtain a good subjective performance.
PL
Odsłuch słuchawkowy w porównaniu z odsłuchem przez głośniki wprowadza zmiany w postrzeganej atmosferze akustycznej i przestrzenności nagrania (efekt internalizacji). Można to zmienić korzystając z technologii HRTF (ang. Head Related Transfer Function). W niniejszym artykule przedstawiono koncepcję procesora słuchawkowego wykorzystującego dwuuszne odpowiedzi impulsowe pomieszczenia (BRIR) mierzone w konkretnym pomieszczeniu odsłuchowym przez końcowego użytkownika systemu. Przeprowadzono badania dotyczące wpływu akustyki pomieszczenia, długości użytych BRIR i jakości elektroakustycznego toru pomiarowego na skuteczność działania procesora. Głównym celem tych badań było określenie minimalnych wymagań, jakie musi spełnić proponowany algorytm, aby zapewnić zadowalające efekty subiektywne.
10
Koncepcja numerycznego modelu głowy do stymulacji HRTF
Plaskota P.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
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2004
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Vol. 85, nr 29
161-166
PL
W artykule przedstawiono koncepcję geometrycznej części numerycznego modelu głowy, który będzie wykorzystany do numerycznego wyznaczania Head-Related Transfer Function (HRTF). Przedstawiono morfologiczne cechy głowy ludzkiej oraz budowę ucha zewnętrznego. Uzasadniono wybór lub pominięcie cech morfologicznych przy konstruowaniu geometrycznej części modelu.
EN
In this paper a conception of the geometrical part of numerical model was introduced wich will be used to numeric marking of Head-Related Transfer Function (HRFT). Morphological guilds of human head as well as the structure of outer ear were pointed out. Choosing or omission morphological features were mentioned at constructing the geometrical part of the model.
11
Headphone processor based on individualized head related transfer functions measured in listening room
Mickiewicz W., Sawicki J.
Prace Naukowe Instytutu Telekomunikacji i Akustyki Politechniki Wrocławskiej. Konferencje
|
2004
|
Vol. 85, nr 29
101-109
EN
Listening by headphones in opposition to a loudspeaker reproduction introduces changes in the perception of acoustic atmosphere and spaciousness (lateralization effect). This can be improved using the Head Related Transfer Function (HRTF) technology. In contrast to previous works we propose a method based on the individualized HRTFs measured simply by the end-user in the acoustic conditions of listening room using own hi-fi set. It gives better subjective results even using standard equipment and a proper post processing (equalization) then available on the market products based on non-individual filters. We present an idea based on individualized Head&Room Related Transfer Function, the algorithm and technical details of individualized headphones processor. All necessary processing can be done in DSP or FPGA to create an PC-independent consumer-electronics unit.
PL
Odsłuch słuchawkowy w porównaniu z odsłuchem przez głośniki wprowadza zaburzenia w przestrzennym odbiorze dźwięku (efekt lateralizacji). Do usunięcia tych niekorzystnych zjawisk stisuje się technologię opartą o funkcje HRTF (ang. Head Related Transfer Function). W odróżnieniu od wcześniejszych prac w artykule przedstawiono koncepcję procesora słuchawkowego bazującego na funkcjach przejścia mierzonych indywidualnie przez użytkownika docelowym pomieszczeniu odsłuchowym z wykorzystaniem własnego zestawu hi-fi. Takie podejście daje lepsze efekty subiektywne w porównaniu z produktami bazującymi na uśrednionych funkcjach HRTF. Zaprezentowany system pomiaru i przetwarzania sygnału może być zaimplementowany z wykorzystaniem procesora DSP lub układu FPGA i stanowić niezależne urządzenie.
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