Virtual Acoustics and 3-d Sound in Multimedia Signal Processing

In this work, aspects in real-time modeling and synthesis of three-dimensional sound in the context of digital audio, multimedia, and virtual environments are studied. The concept of virtual acoustics is discussed, which includes models for sound sources, room acoustics, and spatial hearing. Real-time virtual acoustics modeling is carried out using a real-time parametric room impulse response rendering technique proposed by the author. The algorithm uses a well-known time-domain hybrid model, in which the direct sound and early energy are modeled using geometrical acoustics, and di use late energy is modeled using a recursive reverberator. Sound source directivity, and dynamic room acoustical phenomena such as time-varying early re ections from boundary materials and air absorption are incorporated in the image-source model using low-order digital lter approximations. A novel technique for estimation of source directivity based on the reciprocity method is introduced. Optimization of binaural systems is discussed. Novel methods for head-related transfer function approximation based on frequency warping and balanced model truncation are proposed by the author. Objective and subjective methods for estimating the quality of virtual source generation in headphone listening are introduced. For objective analysis, a binaural auditory model is used, which predicts well the expected performance of di erent lter designs. Subjective listening tests have been carried out to compare design techniques. The results show that binaural lter design based on auditory criteria results in more eÆcient and more perceptually relevant processing. This is the main result of the thesis. Crosstalk canceled loudspeaker reproduction of 3-D sound is reviewed. Stereo widening and virtual loudspeaker algorithms are discussed. An eÆcient, highquality design method of virtual surround lters for playback of multichannel audio on two loudspeakers based on a warped shu er structure is presented. The performance of the method has been veri ed in subjective listening tests. The methods and results presented in this thesis are applicable to digital audio signal processing in general, and especially to implementation of virtual acoustic environments in multimedia and virtual reality systems.