Hideo Shibayama

A study on the technique using fractal dimension in the selection of the kind of sound

There is a paper which described that the selection of the sound which has a different fractal dimension is possible by aural. The fractal dimension of each short time window of conversation sound was analyzed, referring to the paper. In this paper, we showed about the technique using fractal dimension in the selection of the kind of sound. The analyzed sound was a conversation sound with which the engine sound and the chirp sound mix. The value of fractal dimension in the case of the chirp sound of bird or the engine sound indicated a value different from the fractal dimension in the case of the conversation sound. We thought that our technique has shown the characteristic of sound source by one parameter. It is possible to use the fractal dimension to judge a mixing surrounding sound in the teleconference at the direction of the speaker where the voice was used. To transmit a clear voice in the teleconference, the voice is utilized to the estimation in the direction of the speaker. In the real system, t...

An experiment for signal identification of the MIMO communication by sonic waves

Recently, the communication method by MIMO works in a field of the wireless communication. We do research on application to the MIMO system in an acoustic field by sonic wave. As the transmission method, we use the space division multiplexing (SDM) that is the method for the purpose of the improvement of the transmission rate that accepted the number of the transmission elements by sending plural signals at the same time. It is important to identify each signal from several different signals that are transmitted at the same frequency band. And, we study method for detecting each signal. This paper describes influence of the signal detection for the different conditions of the multi‐path propagation.

Estimation for vibration mode of membrane by NAH method

Near Field Acoustic Holography (NAH) is the method of measuring sound information on the radiant surface in the near field as a hologram. By use the technique, we can visualize the vibration of the radiant surface. Thus, we can easily understand the object of the acoustic conditions in acoustic image processing. We made the measurement on one side of the drum using array microphone while the driven source is attached to the other side. In addition, the measurement is not touched on the vibrating membrane surface. This paper describes the estimated results of the vibration mode on the vibration membrane of a drum. And this is possible by apply it to the vibration controlling field for detecting the sound structure on the membrane.

Estimation of reflection location by the correlation coefficient function

Gas is supplied to households through gas pipes that branch out from a main pipe. It is essential to carry out maintenance of these branch pipes to ensure the safe supply of gas. However, there are many cases in which the state of buried gas pipes and the connection condition of a large number of pipes are unknown because no detailed information is included in piping drawings or only plan views are available. If the piping arrangement can be estimated on the basis of response waves originating from an acoustic wave travelling in a gas pipe emitted by a loudspeaker, which is placed at one end of the pipe, this method will be important for the maintenance of branch pipes. To realize this, we report a method of estimating the length of gas pipes using correlation coefficient between a driving signal and measured waves. And, we show the experimental results with high accuracy.

The estimation of the room acoustic characteristic using the acoustic intensity method

When a sound radiates in rooms, a lot of reflection sounds are generated. From estimation of the direction where the room reflection sound comes from, we can understand the diffusion situation in the room acoustic field. By using the acoustic intensity method, we can measure the strength and the direction of the sound. In this paper, we estimate the direction of the reflection sound in the time‐space by the acoustic intensity method and show the acoustic characteristic of the room.

The acoustic information extraction of the indoor impulse response by multiresolution analysis

The impulse response is divided into approximation and detail components by the multiresolution analysis. The correlations between the early sound and reflected sounds are estimated respectively for the impulse response and the approximate signal. The approximate signal was calculated as a function of level of the multiresolution analysis. The correlation coefficient of these correlations is over 0.7 under level three. We evaluate the differences of these correlations from the listening test.

The complexity of environmental sound as a function of seasonal variation

Residential land is performed for a surrounding area of a suburban local city. As a result of urbanization, an area of rich natural environments became narrow. For the animals and plants for whom a river and a forest are necessary, it becomes difficult to live. Environmental sound produced by the tiny insects in this area is changing from year to year. Catching the conditions for the developmental observations and environmental preservation in natural environments, we continue to measure the environmental sound as the time‐series data. We estimate the complexity for these waveforms of the measured environmental sound in the season when insects chirp and do not chirp. For estimation of the complexity, we evaluate by the fractal dimension of the environmental sound. Environmental sound in early autumn is mainly generated by insects in the grass and on the trees. And, the fractal dimension for the sound waveforms of chirping of insects is up to 1.8.

Detection for the early reflection in the impulse response by the correlation function

Detecting an early reflection sound contained in the impulse response measured in a room, we calculated the correlation factor between the early reflection and the impulse response. Calculating the correlation factor every sampling period, we make the correlation function. For the function, we set a threshold level. We detected the absolute correlation value larger than the threshold level. And, we set the zero value for subthreshold level. Following this algorithm, we generate a new signal with the high correlation factor for the early reflection. We compared the signal with the impulse response by using listening test.

Pulse discharge sound source and its application to acoustic measurement

This paper describes a pulse discharge sound source without any diaphragm, and its application for acoustic measurements. The waveform of the sound pulses radiated from this source is simple and reproducible. The power spectra of these pulses have no zero points up to 90 kHz. The duration of the sound pulse is about 50 uμs, and is dependent on the gap length between the discharge electrodes. The directivity function of the sound source is the same as that of a line source that is equal to the gap length. The sound generating spot is small, and the sound source requires no baffle board. As a result, no reflection from the sound source itself is produced. The timing of sound generation is stable and controllable. As examples of acoustic measurements utilizing the sound source, the estimated results of acoustic impedance characteristics of materials and their frequency responses of diffraction are shown. The estimated results agreed well with the calculated ones. A measuring system can be considerably simpli...