Julio C. B. Torres

Hybrid method for numerical simulation of room acoustics with auralization: part 1 - theoretical and numerical aspects

A new hybrid simulation method for room acoustics is presented. It is grounded on two well known numerical simulation techniques for room acoustics. The hybrid method takes geometric acoustics for granted and uses an improved version of the classical ray-tracing technique for computing the specular reflections and a slightly modified energy transition method for simulating the diffuse reflections. The impulse responses (IRs) are then computed by superposition of the specular and diffuse ones. The reverberant part of the IRs gains a much more realistic aspect than the one obtained from either ones method alone. Both the ray-tracing technique and the energy transition method are reviewed and some improved features are discussed. The sound source and the receiver modeling are presented, including a new method for simulating the head related transfer functions (HRTFs), and based on the wavelet technique, which provides a shorter time computation of the binaural impulse responses for auralization purposes. In a companion paper, entitled Hybrid method for numerical simulation of room acoustics: Part 2 - Validation of the computational code RAIOS 3, a validation of the method in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones.

Low-order modeling of head-related transfer functions using wavelet transforms

In this paper, an efficient method for modeling head-related transfer functions (HRTFs) of an auralization system is presented. The proposed model is based on the decomposition of the impulse response of the HRTFs by wavelet transforms. Through an analysis of the HRTF energy content per subband it is shown how the model can be reduced without introducing considerable error in the magnitude and phase frequency responses. As a result of the proposed technique, the low-order model has approximately 30% of the number of coefficients of the original HRTF, which represents an important reduction in the computational cost of an auralization system implementation.

Low-order modeling and grouping of HRTFs for auralization using wavelet transforms

An efficient method for modeling head-related transfer functions (HRTFs) of an auralization system is presented. The proposed model is based on the decomposition of the impulse response of the HRTFs by wavelet transforms and on the grouping of such functions for close directions. Through an analysis of the HRTF energy content per subband, it is shown how the model can be reduced without introducing considerable errors in the magnitude and phase frequency responses. As a result of the proposed technique, a significant reduction in the processing time of the auralization process is obtained by a low-order model which has approximately 30% of the number of coefficients of the original HRTF and by a reduction in the number of HRTF directions to less than 10%.

HRTF interpolation in the wavelet transform domain

This paper presents a new HRTF (Head Related Transfer Function) interpolation technique for three-dimensional sound generation. The proposed approach is based on the determination of the optimal weights to be applied to the HRTF coefficients of neigh-boring positions in the wavelet domain in order to obtain the HRTF at a given point. The proposed method is compared to conventional interpolation methods through the error analysis of the HRTFs in the frequency and time domains. It is verified that the proposed method presents smaller interpolation errors for all HRIRs (Head Related Impulse Responses) of an available database.