Study On Binaural Auralization Quality And It's Influenced Factors

Auralization is a process to model the sound field where listener presented by physical or mathematical methods and reproduce the modeling sound signals, in such way to simulate the binaural listening experience at a given sound field. Binaural auralization which refers specially to auralization implemented by binaural reproduction, is the most popular auralization technique. Binaural auralizaion was widely used in subjective evaluation of auditorium quality, virtual auditory experiment, virtual reality. In actual applications, however, it was found that auralizaiton effect differed from listening experiences in real environment, which attracted international research interesting. Relative to auralization application, research on the factors affecting binaural auralization quality was seldom. Many problems has not reach common conclusion yet. Systematic research on this area has not been reported in domestic literatures.First, research progress on auralization and factors affecting auralization quality were reviewed and binaural room impulse response (BRIR) measurement methods were addressed. Then the effect of sound source directivity, individualized binaural room impulse response and headphone reproduction of binaural signal on binaural auralizatioin quality was studied.Because of acquiring BRIR by measurement in this paper, the measurement methods using maximum length sequences (MLS) was specified in chapter 2. Factors affecting MLS measurement were analyzed. Based on this, several methods were proposed to improve MLS measurement accuracy, including reducing non-linear distortion, avoiding time-variation during measurement and improving signal to noise ratio.In the aspect of sound source directivity, a dodecahedron sound source and directional sound source were employed to measure room impulse response (RIR) and BRIR, and then auralization quality generated by these two kinds of sound sources were analysed by objective and subjective comparisons. Objective comparison shows that sound source directivity almost has no effect on T30,EDT and has significant effect on C80,STI,IACC. Subjective comparison shows that the subjective distance produced by directional sound source is nearer than that produced by omni-directivity source and that directional sound source can generate clearer subjective perception.Listening test was carried out to compare the differences between individualized and non-individualized BRIRs in auralization. Results show that, subject can discriminate the differences between these two kinds of BRIRs mainly using timbre cue. The timbre difference mainly ocured at high frequencies over 6 kHz. Therefore, the effect of individualized BRIR on binaural auralization can not been neglected (especially for the situation that signal has abundant high-frequency energy), and the use of individualized BRIR is nesseceray for binaural auralization.Moore's binaural loudness model was used to compare the loudness spectra difference between individualized and non-individualized BRIRs. Results show that binaural loudness spectra differences mainly occur at high frequencies, especially at the frequency range of 34～36 ERB number(8.6 kHz ~10.7 kHz). This is primarily due to the fact that the pinna notch frequency is different from subject to subject. Binaural loudness spectra differences all exceeded 1 phon/ERB. This indicates that the differences were audible and verified the results of the previous listening test.While studying front-back confusion of image localization, it was found that, under the experimental condition in this paper, the performance of front-back image discrimination in individualized auralization was not better than that in non-individualized auralization. From this result, it can be seen that utilizing individualized BRIR was not enough to solve the front-back confusion problem.Three kinds of headphones were employed to examine headphone transfer function (HpTF) measurement repeatability. Result shows that measurement repeatability depends on the degree of pinna distortion due to headphones'covers pressing pinna. In binaural auralization, it was recommended to use circumaural headphones with larger cavity.In last, effectiveness and weakness of non-individualized headphone transfer function (HpTF) compensation was studied. Results show that, improper non-individualized HpTF compensation can produce negative effect on auralization quality, especially on high-frequency timbre of auralization.The research results can provide ideas and experimental data to improve binaural auralization.