Sunmin Kim

Real-time estimations of multi-modal frequencies for smart structures

In this paper, various methods for the real-time estimation of multi-modal frequencies are realized in real time and compared through numerical and experimental tests. These parameter-based frequency estimation methods can be applied to various engineering fields such as communications, radar and adaptive vibration and noise control. Well-known frequency estimation methods are introduced and explained. The Bairstow method is introduced to find the roots of a characteristic equation for estimations of multi-modal frequencies, and the computational efficiency of the Bairstow method is shown quantitatively. For a simple numerical test, we consider two sinusoids of the same amplitudes mixed with various amounts of white noise. The test results show that the auto regressive (AR) and auto regressive and moving average (ARMA) methods are unsuitable in noisy environments. The other methods apart from the AR method have fast tracking capability. From the point of view of computational efficiency, the results reveal that the ARMA method is inefficient, while the cascade notch filter method is very effective. The linearized adaptive notch filter and recursive maximum likelihood methods have average performances. Experimental tests are devised to confirm the feasibility of real-time computations and to impose the severe conditions of drastically different amplitudes and of considerable changes of natural frequencies. We have performed experiments to extract the natural frequencies from the vibration signal of wing-like composite plates in real time. The natural frequencies of the specimen are changed by added masses. Especially, the AR method exhibits a remarkable performance in spite of the severe conditions. This study will be helpful to anyone who needs a frequency estimation algorithm for real-time applications.

KAIST interactive bicycle racing simulator: the 2nd version with advanced features

This paper presents the KAIST interactive bicycle racing simulator system, which consists of a pair of bicycle simulators. The rider on the racing simulator experiences realistic sensations of motion, while being able to see the other bicycle simulator and having the audio-visual experience of riding in a velodrome or on the KAIST campus. The 2nd bicycle of the racing simulator system consists of a bicycle, a 4-DOF platform, a handlebar and a pedal resistance system to generate motion feelings; a real-time visual simulator a HMD and beam projection system; and a 3D sound system. The system has an integrating control network with an AOIM (Area Of Interest Management) based network structure for multiple simulators.

Confirming the perception of virtual source elevation effects created using 5.1 channel surround sound playback

Employing an array of nine speakers, five of which were at the listeners ear level, and four of which were elevated well above the listeners ear level, an experimental investigation of virtual sound source elevation was completed in each of three reproduction environments. The primary question of interest was that regarding whether the elevation of virtual sound sources could be modulated in a simple fashion using only the five ear-level speakers that form a conventional 5.1 channel surround-sound speaker layout [ITU-R. BS. 775-1. 1994]. It was found that the creation of elevated virtual sources was possible using the two surround-channel speakers or using all five ear-level speakers, and the resulting elevated virtual source imagery was compared with the source imagery associated with sound reproduced via speakers that were actually well elevated above the listeners ear level. Besides the extremely dry listening conditions of the anechoic chamber, tests were completed in a reverberation chamber, and in a moderately dry audio surround production studio, typical of the controlled acoustics featured in many critical listening spaces. The fact that similar results were observed in each of three listening environments supports the conclusion that the observed results are not idiosyncratic to any particular environment, such as the anechoic chamber, but results will likely generalize across many environments.

An effective design method of inverse filters for multichannel 3D sound rendering

Provides an effective design method of inverse filters for use in multichannel 3D sound rendering. In order to obtain the optimal solution of the inverse filter, the conventional adaptive algorithm requires that the parameters are properly tuned through lots of time and effort while through the proposed method we can systematically obtain the inverse filter with the desired accuracy and very low computations. In the z-domain, we approximately design the stable inverse filters of a maximum phase system in order to solve the inverse problem of a multiple-input-multiple-output nonminimum phase system. We compare the proposed method with the conventional one based on the adaptive algorithm through computer simulations.

New 3D audio for ultra high definition digital TV; loudspeaker configuration and method for virtual elevation effect rendering

This paper suggests the next-generation audio system for ultra high definition digital TV in terms of loudspeaker layout and corresponding rendering method. First part introduces the listening test results of perceived audio quality with several loudspeaker arrangements in order to find the optimal configuration of loudspeakers for a next-generation multichannel sound system. The subjective evaluations focused on the loudspeaker configurations at the top layer were carried out with test materials by mixing in studio and from B-format recordings. The results show that the perceptual difference in the overall quality achieved with the new 10.2-channel vertical surround system with 3 top loudspeakers and the reference system was imperceptible. Second part presents the virtual elevation effect rendering algorithm which can give a listener an impression of virtual 10.2 channel speakers using the conventional 7.1 channel speaker system (ITU-R BS.775-2) placed in horizontal plane. The proposed virtual height spe...