Nobuharu Aoshima’s research while affiliated with University of Tsukuba and other places

A frequency and reverberation response of a circular pipe resonator are studied by newly developed techniques of the signal compression method and the calculation method of reverberation response from impulse response. By these methods, reverberation decay curves for very narrow band input signals are obtained and dips in reverberation curves are observed. These dips appear when two frequency response peaks are influenced equally by narrow band input signals. These measuring methods would be useful for room acoustics when fine structure of reverberation decay curve is desired.

Signal compression method was applied for a measurement of wind effects to a sound attenuation by a barrier. This method uses special computer generated test signal, which can be compressed to a pulse like signal by a numerical phase shift filter. External noise can be reduced and effects of reflected sounds can be eliminated by this method, so it is suitable for a measurement of sound attenuation in noisy air flow conditions. Experiments were performed in rather small test room for short propagation path length. Obtained signals and computer processed waveforms are illustrated with the results of attenuation characteristics for five wind conditions.

Influences of energy and particulate matter were experimentally reduced by eliminating the upper part of the euphotic zone, using a large sediment-seawater enclosure (SSE)in situ in Saanich Inlet, B.C., Canada. The standing stock of heterotrophic microorganisms, as determined by ATP concentration, in the experimental dysphotic zone was not appreciably affected, although the decreased supply of organic material did reduce their rate of nutrient uptake from the environment. In the mesotrophic level of the natural dysphotic zone, the turnover rate of glutamic acid remained near the initial rate by readjusting into a new balance.

A computer-generated pulse signal for sound measurement is discussed. A pulse signal whose power spectrum is flat is generated by inverse Fourier transformation. The generation of a time-stretched pulse and its compression method are also considered. Computer-controlled measurements enable time averaging and the elimination of reflected sound is made in the computer memory by the operator's instruction monitoring acquired waveform on CRT.