Tsuneji Koshikawa

Object recognition system

An object recognition system wherein, in order to derive the features of an object to-be-recognized such as shape and size from a reflected wave or echo, the ratio between a signal obtained by Fourier transforming a part of a transmitting wave for the object and a signal obtained by Fourier transforming a received reflecting wave is subjected to the inverse Fourier transform so as to obtain separate reflection signals corresponding to a large number of reflecting points of the object, whereby the features of the object are recognized by utilizing the reflection signals.

Solid‐liquid compound hydroacoustic lens of low aberration

With the intention of improving the resolving power of underwater acoustic imaging systems, hydroacoustic lenses of the solid‐liquid compound type were investigated with special attention to their aberrations and F number. The solid and liquid materials used were, respectively, a plastic and a silicone fluid, thus forming an interface of higher refractivity than those between a plastic and water, or a silicone and water. The ray‐tracing computations of the aberration showed that the meridional and sagittal aberrations of the solid‐liquid compound lens of aspherical type designed and constructed in the present research were much reduced. The results of measurements on Fraunhofer diffraction patterns showed that an F number as small as F/1.0 was realized by the solid‐liquid compound lens of aspherical type, and this in turn considerably improved the least resolvable separation on the focal plane of the lens for a given sound wavelength, and the resolving power of the lens for a given sound wavelength and a ...

Correlations between sound field characteristics and subjective ratings on reproduced music sound quality

The partial‐space power, a sound field property for a loudspeaker, was newly defined in order to obtain general characteristics including on‐axis sound pressure and total‐space power. For typical loudspeakers, it was confirmed that the partial‐space‐power frequency response reflects the principal features, dips, peaks, and gradients of space‐averaged sound‐pressure frequency response in ordinary rooms. An all‐inclusive listening test was performed with six subjective rating scales for ten loudspeakers. Then, the correlation between the sound field characteristics and the subjective rating data were examined. The sound dispersion as well as the frequency response seems to correlate with most normally employed subjective rating scales used in listening tests.

Real‐Time Colored Display of Sound Spectrogram

If signal spectrograms are displayed in real time, so‐called brightness modulation display is used in general. Because of the limited dynamic range of brightness modulation of CRT, details of the spectrum are lost very often. In order to overcome such defects and be able to observe instantaneous spectrum patterns more clearly and easily, we constructed new display apparatus in which effective use of visual function is considered. In this system, instantaneous spectrum amplitude is quantized in 11 levels with the step of 4 dB, and each amplitude level is converted to predetermined hue resembled to contour map. Furthermore, these colored instantaneous spectrograms are memorized in sky‐sign like fashion in a certain time interval. As the results of displaying various acoustic signals, it is confirmed that color display of this type is more useful than monochromatic display for the visual discrimination of the characteristics corresponding to each signal differences.