Realization Of Auralization By Finite-Difference Time-Domain Method With Improved Boundary For Room In Low Frequency

Auralization can simulate the actual hearing environment. By reproducing sound through high-fidelity headphone or speakers, lifelike sound environment can be reconstructed. When auralization is used in architectural acoustic designs, sound quality of spaces can be estimated and assessed by designers through auralization that if it is within a desired level, just before the building is under construction. For the important acoustic design clues the auralization can provide, the realization techniques of auralization are the main investigation aspects of this paper. To obtain the binaural room impulse response (BRIR) through simulating acoustic soundfiled by computer is the main aspect of auralization technique, for such reason, a simulation model based on wave acoustic theory is established. BRIRs are calculated and auralization is realized by the model, which is established by finite-difference time-domain method (FDTD).For accurate boundary is essential to the validity of FDTD model, related boundary models are investigated in details, which include idealistic hard boundary, absorbing boundary, simplified impedance boundary and complex impedance boundary. Sound or wave effects caused by the boundaries are investigated as well, such as the acoustic problems of sound aperture and barrier. Especially, for the frequently used absorbing boundary of perfectly matched layers (PML), the effects of layers amount and attenuation coefficient on the absorbing ability of PML in FDTD model are investigated. The computation results reveal that more PML layers bring fewer reflections though increase computation burden; when layers amount is unchanged, attenuation coefficients should be in appropriate values to decrease attenuation difference, so as to restrain reflections; practical methods to decide proper layers amount and attenuation coefficients are suggested, and they are verified by some acoustic models.Complex impedance model contains information that reveals phase, amplitude and their frequency-dependant characteristic. FDTD expressions of complex impedance boundary are described in the form of infinite impulse response (IIR) digital filters. Gaussian pulse stimulus and its according inverse filter are built into FDTD complex impedance model of a real small room, and RIRs are calculated and verified by measurement, which is carried in a real room. The results prove the validity of the FDTD model, which is precondition for realizing auralization.Subjective hearing experiment is finally designed to verify the auralization. BRIRs of the real room are measured on a custom-made hard spherical head, and such BRIRs, also with the calculated ones, are convoluted with dry signals of white noise, voice and music, so as to be used in the subjective hearing. The results reveal that both RIR and BRIR models can be used in the auralization of voice and music signal within low frequency. From the hearing experiment of white noise, human head is found to be related to hearing results, so as to be a factor in room auralization.On achievements and practical meanings of investigation as mentioned above, the conclusions of how the absorbing ability of PML layers is effected by layers amount and attenuation coefficient, and the deciding of layers amount and attenuation coefficient have practical meanings to acoustic investigation of room with open doors or windows.On the establishment and verification of FDTD IIR complex boundary model, they provide more detail physical descriptions to the boundaries used in FDTD model based on wave acoustics. The verification by subjective hearing experiments, include mono and stereo hearings, reveal the auralization qualities in different frequeny regions. Hearing experiment also validates the auralizatioin in voice and music signal, and estimates that to incorporate head factor in room model will further improve the binaural auralization.