Tacksung Choi

Virtual Sound Rendering in a Stereophonic Loudspeaker Setup

This paper presents a mathematical analysis of the effects of interchannel amplitude and time differences in two channel (stereophonic) sound systems. The analysis is developed by computing the acoustic conditions at the listeners ears as a function of the stereophonic signal feature. We also present separate approximations of head-related transfer function (HRTF)-based panning according to predefined frequency bands. We attempt to create non-sophisticated models of the stereophonic listening mechanism with approximations in both the time and frequency domains. The models are based upon psychoacoustical theories that present the frequency-dependent relative importance of acoustical cues. Based on the model, we propose new panning methods that can enhance the localization accuracy of conventional panning methods, such as amplitude panning and HRTF-based panning. The localization performances of the new panning techniques are evaluated and compared by means of auditory model simulations and listening tests. Through simulations and listening test results, it is shown that the proposed panning method makes substantial improvements in the localization of virtual sources.

Design of Time-Varying Reverberators for Low Memory Applications

Development of an artificial reverberator for low-memory requirements is an issue of importance in applications such as mobile multimedia devices. One possibility is to use an All-Pass Filter (APF), which is embedded in the feedback loop of the comb filter network. In this paper, we propose a reverberator employing time-varying APFs to increase the reverberation performance. By changing the gain of the APF, we can increase the number of frequency peaks perceptually. Thus, the resulting reverberation sounds much more natural, even with less memory, than the conventional approach. In this paper, we perform theoretical and perceptual analyses of artificial reverberators employing time-varying APF. Through the analyses, we derive the degree of phase variation of the APF that is perceptually acceptable. Based on the analyses, we propose a method of designing artificial reverberators associated with the time-varying APFs. Through subjective tests, it is shown that the proposed method is capable of providing perceptually comparable sound quality to the conventional methods even though it uses less memory.