Statistical evaluation method of monosyllabic voice identification rate is developed in order to investigate the characteristics of consonant identification and to find the optimal parameters in our voice recognition system. In our system, every monosyllable is converted into a time spectral pattern with 16 components in frequency and 16 components in time after procedures of an envelope matching, an extraction of a consonant, a time smoothing and a level normalizing. Each input pattern is refered to standard patterns following the same vowel as the input by means of the minimum square distance classification. Every input pattern is represented as a matirix X which is an element of a population of each monosyllable G_i (i≤15) which is supposed to be obeyed to a multi-dimensional normal distribution, and the error rate is estimated from the probability P_b(j/i) in which X in G_i belongs to the space of G_j beyond a discriminating plane between two populations G_i and G_j. From experimental results by 30x15 monosyllables following vowel /a/ pronounced by a male speaker aged 25, characteristics of the estimated error rate coincides with that of an experimental data, our envelope matching method is proved to have almost the same effect as the shift matching, and the optimal values and method are obtained with respects to an extraction part of consonant, window length of the time smoothing and the level normalizing method by calculating the error rates in various parameters. Furthermore, it is found that the unvoiced plosives /k/, /t/ and /p/ have the different optimal parameters from the other consonants in the above evaluations, so that the different pre-processing method will be needed for the unvoiced plosives in order to make the identification rate increase.
High-frequency acoustical fields excited in a concave rigid wall by a source located on the wall surface are described. Acoustical pressure fields can be expressed in alternative representations:(1) a combination of Whispering Gallery modes and continuous spectrum and (2) a combination of acoustical rays and Whispering Gallery modes. The analysis is performed by an asymptotic evaluation of the rigoriously formulated Green's function. Pressure fields are expressed in the 3-dimensional projection, as parameters of circumferential distance from the source and radial distance from the wall surface. Strong emphasis is placed on the physical interpretation of the results. Most pleasing from a physical standpoint is a fields solution that comprises a mixture of a few geometric acoustical rays and Whispering Gallery modes.
In this paper, an analytical technique for calculating the amplitude of reflected sound waves from a rigid rectangular body with curved surface is described. This theory is based on the assumption that a receiver is located independently from a transmitter. The formulas for the reflctivity are derived approximately under certain restrictions of geometrical optics. The reflectivity, which is termed "directional sound reflectivity", is defined as the ratio of the reflected sound pressure from a target to the calculated one which is derived the theory of geometrical optics. To verify the validity of the approach, some experiments were performed in air at the frequency of 39. 80kHz. Experimental results showed good agreement between the calculated and the measured values and this confirmed the usefulness of the present technique to calculate the reflection of sound waves from a rigid rectangular body with curved surface.
As is well-known, the wave form of random noise and vibration appearing in our actual enviroment shows usually the variety and the complexity in its fluctuation pattern. The statistical methods of analyzing and evaluating the above random wave form were studied by many researchers, from the viewpoint of signal analysis. In this paper, after first setting a generalized method of statistically evaluating the acuity of fluctuating random wave based on the information on each order of differntial type state variables, especially for the stational random wave of arbitarary distribution type, a new trial toward the statistical evaluation on the locations of level crossing, peak and trough has been concretely considered as the special cases, in close connection with the above differential type state variables. That is, in the proposed theory, the effect of usual linear correlations and non-linear correlations among two and/or many sampled points of random wave on the above probability distribution form of level crossing, peak and trough has been fully discussed under introduction of multivariate joint probability distribution. Finally, the practical effectiveness of the present theory has been experimentally confirmed too by applying it to the acrual road traffic noise wave obeserved ina suburb of a large city.