Mamoru IWAKI

Associate Professor, Dr. Eng.

Information Science and Engineering
Graduate School of Science and Technology
Niigata University

( Department of Biocybernetics Technology
Faculty of Engineering )

NOTE: Japanese page is here.


Research Fields
Speech & Audio Signal Processing, Digital Signal Processing, Approximation & Interpolation Theory

Research Interests (details)
I am interested in theory and implementation of waveform analysis for speech and audio signal processing. My research currently focuses on an instantaneous analysis of waveforms by the natural observation theory and its implementation by digital filters.

Publications (details)
Papers & Letters
Proceedings of Intl. Conf.
Tech. Reports & Others

Others (details)

Last modified on Dec. 24, 1996 by

Research Interests

1. Fundamental Research on Analysis and Recognition of Waveforms
Instantaneous analysis methods of waveforms are investigated based on the Natural Observation Theory proposed by Prof. Iijima. The theory was constructed in the aspect of waveform observation: a waveform can be observed from moment to moment as time goes by. The concept of natural observation method was exported to discrete-time waveforms, and it was implemented on digital computers. Digital filters for synthesis and recognition of waveforms are developed and applied to speech and audio signal processing.

2. Analysis of Individuality in Glottal Vibration
Speech waveforms contain not only phonetic information but also prosody which can express individuality, emotion and so on. In particular, individuality is essential for advanced speech processing in the years ahead. In conventional investigations of individualities, it has become clear that pitch pattern and higher band in spectral envelopes contain an important information of individuality, however, it is still hard to know how the glottal vibration has effects on it. Hence we develop an effective pitch extraction method in order to make the aspect of glottal vibration clear. EGG waveforms from Laryngograph are used as both reference and target signal for analysis.

3. Representation Method of Signals for Digital Signal Processing
Sampling is indispensable for digital signal processing of continuous-time signals. It is hard to realize effective processing without appropriate sampling. Considering all stages of signal processing, i.e. generation, observation, sampling, processing, and output, we discuss a sampling method for effective digital signal processing and its applications.

4. Design Methods and Applications of Digital Filter
Digital filter design method is one of the solutions of optimization problems: the desired impulse response/transfer function is obtained as an approximation function based on a certain optimal criteria, e.g. minimax criteria. Numerical analysis and improvement of Remez-exchange method, which is known as a solution for minimax criteria, are investigated. And simultaneous approximation of amplitude and phase characteristics is also investigated for Linear phase FIR digital filters under the criteria.

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Selections from the Latest Publications

  1. Pluralizing Method of Simple Similarity Based on Natural Observation Method of Normal Type --- with an application to Speaker-Independent Vowel Recognition ---, Trans. IEICE (A), 1997 (In Japanese)(Printing).

  2. On Uncertainty Principle in Natural Observation Transform of Normal Type, Trans. IEICE (A), 1997 (In Japanese)(Printing).

  3. On Uncertainty Principle in Natural Observation Transform of Neighboring Type, Trans. IEICE (A), Vol.J79-A, No.11, 1996 (In Japanese).

  4. Consideration on Derivation Principles of Natural Observation Method of Discrete type, Trans. IEICE (A), Vol.J79-A, No.11, 1996 (In Japanese).

  5. Description of FIR digital filters in the form of parallel connection of linear phase FIRs, Electronics Letters, Vol.32, No.11, 1996.

  6. Natural observation method for discrete-time waveforms, Trans. IEICE (A), Vol.J79-A, No.3, 1996 (In Japanese).

  7. On a Vowel Synthesis System using Natural Observation Method, Tech. Rep. IEICE, SP95-142, 1996 (In Japanese).

  8. Pluralizing Method of Similarity for Speaker-Independent Vowel Recognition, Tech. Rep. IEICE, SP95-141, 1996 (In Japanese).

  9. Fundamental theory of natural observation method with complete reconstruction property by finite sum --- Natural observation theory of normal type ---, Trans. IEICE (A), Vol.J79-A, No.1, 1996 (In Japanese).

  10. Structural analysis for vowel waveforms by using finite Dirichlet series, Tech. Rep. Hear. Acoust. Soc. Jpn., H-94-42, 1994 (In Japanese).

  11. Sampling theorem for spline signal space of arbitrary degree, IEICE Trans. Fundamentals, Vol.E77-A, No.5, 1994.

  12. Polynomial interpolation for Remez exchange method, Electronics Letters, Vol.28, No.20, 1992.

  13. Periodic sampling basis and its biorthonormal basis for the signal spaces of piecewise polynomials, Trans. IEICE (A), Vol.J75-A, No.6, 1992 (In Japanese).


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