Papers by Akinori Nishihara
Electronics and Communications in Japan (Part III: Fundamental Electronic Science)
Electronics and Communications in Japan (Part III: Fundamental Electronic Science)
Digital filters play an important role in multidimensional signal processing. Because the coeffic... more Digital filters play an important role in multidimensional signal processing. Because the coefficients must be expressed in finite wordlength, the deterioration of the characteristics becomes a problem. Using a lattice structure whose efficiency has been confirmed for onedimensional (1-D) digital filters, this paper proposes a unified synthesis method for the practically important separabledenominator multidimensional IIR digital filters. First, the implementation of a 2-D separabledenominator transfer function by a separabledenominator 2-D digital lattice filter is considered. A characteristic of the proposed separable-denominator 2-D digital lattice filter is that both the usual tapped lattice structure and the injection-type lattice structure are used and the signal flow becomes simple compared to the method so far. Next, when the numerator polynomial is a mirrorimage polynomial, an implementation method is presented in which the number of tap multipliers is reduced significantly. Furthermore, a method is suggested for the synthesis of a 3-D transfer function based on the same approach as for the 2-D case. Finally, the efficiency of this method is confirmed by an example.
Electronics and Communications in Japan (Part III: Fundamental Electronic Science)
The circuit with zero sensitivity at the matching points is desirable in the sense that a very lo... more The circuit with zero sensitivity at the matching points is desirable in the sense that a very low sensitivity can be expected in the passband. It should also be noted that the wave digital filter (WDF) with a IIeascade structure has the advantage that the sensitivity in the stopband is lower than WDF with a T-cascade structure. However, the synthesis method has not been known for WDF with a IIcascade structure with the zero amplitude sensitivity at the matching points which can realize an arbitrary transfer function. This paper is an attempt to realize such a WDF. First, it is shown what type of sections should be used as the reference section of a doubly resistor-tenninated reactance filter. The two terminating resistances are set equal to avoid the situation where the sensitivity at the matching point turns out to be nonzero because of the effect of the terminating resistance ratio. Then the replacement of the multiplier is shown so that the forementioned state is maintained, even if the multiplier coefficients are quantized. It is shown that WDF exists corresponding to each section, where the forementioned replacement can be applied and the structural boundedness is retained even after the coefficients are quantized. As a result, it is shown that W D F actually exists with a II-cascade structure with the zero amplitude sensitivity at the matching points which can realize an arbitrary transfer function.
Electronics and Communications in Japan (Part III: Fundamental Electronic Science)
This paper proposes a synthesis of low-sensitivity digital filters which are pipelineable and hav... more This paper proposes a synthesis of low-sensitivity digital filters which are pipelineable and have simple structures. Their sensitivity characteristics are similar to those of wave digital filters. The synthesis of these filters is attained by factorizing paraunitary scattering matrices derived from given zdomain transfer functions without referring to analog filters. The synthesized structures are the T d e connection of fundamental sections which are constructed by using series and parallel sections of wave digital filters. The proposed synthesis method can realize any given IIR transfer function, while previous methods which synthesize T d e d structures can realize only the amplitude response of any given transfer function. In addition, the method can realize the transfer functions of which the order of their denominator is higher than that of their numerator including FIR transfer functions.
Electronics and Communications in Japan (Part III: Fundamental Electronic Science)
Sometimes it is required to change the filter characteristics of a digital filter in real time du... more Sometimes it is required to change the filter characteristics of a digital filter in real time during its filtering operation. To meet this requirement, variable cutoff frequency lowpass filters with real coefficients have been reported using only one parameter. Moreover, variable bandpass filters with complex coefficients have been reported where only one parameter was to be changed and where either the upper or lower band-edge frequency of the passband was fixed. However, in those filters, the frequency response was degraded with the change in characteristics which could not be resolved. l k s paper proposes the synthesis of a variable IIR digital filter using one parameter and the frequency response is not degraded when the characteristics are changed. In the variable filter proposed here, the cutoff frequency and the bandwidth may be changed without any restriction. Moreover, a simple circuit realization technique is proposed so that the filter circuit may actually be implemented. In this technique, any type of real coefficient filter circuit may be used as the prototype filter. Finally, the simulation of the synthesis problem is carried out and the validity of the proposed method is confirmed.
Issues in Informing Science and Information Technology
An algorithm learning tool was developed for an introductory computer science class in a speciali... more An algorithm learning tool was developed for an introductory computer science class in a specialized science and technology high school in Japan. The tool presents lessons and simple visualizations that aim to facilitate teaching and learning of fundamental algorithms. Written tests and an evaluation questionnaire were designed and implemented along with the learning tool among the participants. The tool’s effect on the learning performance of the students was examined. The differences of the two types of visualizations offered by the tool, one with more input and control options and the other with fewer options, were analyzed. Based on the evaluation questionnaire, the scales with which the tool can be assessed according to its usability and pedagogical effectiveness were identified. After using the algorithm learning tool there was an increase in the posttest scores of the students, and those who used the visualization with more input and control options had higher scores compared...
ICASSP '86. IEEE International Conference on Acoustics, Speech, and Signal Processing
ABSTRACT A sufficient condition for the absence of limit cycle oscillations is studied, and a new... more ABSTRACT A sufficient condition for the absence of limit cycle oscillations is studied, and a new relaxed condtion is proposed. Then a method to derive digital filter structures, which satisfy this condition, from a given form of secondorder transfer function is presented. Several new ...
IEEE Transactions on Circuits and Systems
EURASIP Journal on Audio, Speech, and Music Processing
This paper proposes a new speech enhancement (SE) algorithm utilizing constraints to the Wiener g... more This paper proposes a new speech enhancement (SE) algorithm utilizing constraints to the Wiener gain function which is capable of working at 10 dB and lower signal-to-noise ratios (SNRs). The wavelet thresholded multitaper spectrum was taken as the clean spectrum for the constraints. The proposed algorithm was evaluated under eight types of noises and seven SNR levels in NOIZEUS database and was predicted by the composite measures and the SNR LOSS measure to improve subjective quality and speech intelligibility in various noisy environments. Comparisons with two other algorithms (KLT and wavelet thresholding (WT)) demonstrate that in terms of signal distortion, overall quality, and the SNR LOSS measure, our proposed constrained SE algorithm outperforms the KLT and WT schemes for most conditions considered.
The Journal of Information and Systems in Education
This study adopted eye-tracking techniques to investigate the viewing behaviors of students when ... more This study adopted eye-tracking techniques to investigate the viewing behaviors of students when they watched a slide video in order to get a better understanding of slide video design and learning style theory. The Felder-Soloman Learning Style Model (FSLSM) was used to test students' learning styles and students' viewing behaviors were recorded by an eye-tracking machine. Results showed that participants tended to give priority to the text parts which was consistent with the literature. Pictures in the slide video were paid attention to in a higher ratio compared with a previous study on text-picture integrated stimulus. Effects of slide features and picture functions on students' viewing behaviors were examined. Strong visual learning preference participants paid more attention to the picture and title parts. Moderate visual participants paid more attention to the text and video parts while well-balanced participants were in between them. Sequence analysis was applied to check the transition preference and similarities of viewing behaviors among students. Strategies on slide video designs and a discussion of FSLSM model are provided.
EURASIP Journal on Audio, Speech, and Music Processing
1988., IEEE International Symposium on Circuits and Systems
Ieice Transactions on Fundamentals of Electronics Communications and Computer Sciences, Apr 25, 1997
電子情報通信学会ソサイエティ大会講演論文集, Sep 2, 2008
Journal of Educational Multimedia and Hypermedia, Nov 1, 2012
Ieice Transactions on Fundamentals of Electronics Communications and Computer Sciences, Jun 1, 2003
電子情報通信学会ソサイエティ大会講演論文集, Sep 2, 2008
Itc Cscc International Technical Conference on Circuits Systems Computers and Communications 제2권, 1998
Electronics Letters, Feb 1, 1985
Uploads
Papers by Akinori Nishihara