In order to analyze the articulation mechanism of a talking bird "Mynah, " mimic voices obtained in He- O_2 atmosphere are compared with those in the normal air based on the frequency analysis by linear prediction. A mixture of 80%-He and 20%-0_2 at one atm is used in the experiment of helium voices, and 36 mimic voices consisted of words are recorded by a taperecorder in both cases. Comparing vowel parts of normal voices with those of helium voices, it is found that the spectrum pattern of mimic voices has two types, I and II, about the structure of spectral envelope peak components. Type I shows the frequency shift in helium atmosphere and type II shows no frequency shift. Spectral envelope peak components of type I appear around 0. 8-1. 2kHz, 1. 8-2. 4kHz and 3. 8-4. 4kHz, and their frequencies do not change with vowels. On the other hand, the component of type II appears in the range from 1. 5 to 3kHz and its frequency changes with vowels. It is ascertained that (1) only the spectral envelope peak components of type I show almost the same frequency shift as those estimated by the formula describing theoretical transformation of peak frequencies, (2) spectral envelope peak frequencies of type I coincide with resonance frequencies obtained by twin-tube model of which parameters correspond to the vocal tract of Mynah, (3) the number of observed spectral envelope peaks are beyond that of the resonances calculated by twin-tube model, and (4) the observed spectral envelope coincides with one which is obtained by adding a component of type II to the spectral envelope estimated from the source-system model using spectral envelope peaks of type I as poles. From above results and analyses, it is confirmed that type I has multi peak components which are formed by resonances of the vocal tract, and type II has a single peak component which may not be formed by the resonance. Furthermore, it is assumed that Mynah's syrinx may produce two components as sound sources. The first one has a wide range spectrum composed of pitch and its harmonics, which is similar to the sound source by human's vocal cord. The second one has a higher frequency component corresponding to type II. This hypothesis may be also supported by the anatomical structure of the syrinx. From above considerations, it is concluded that Mynah may produce the vowel part of mimic voices by controlling the frequency of the second sound source in addition to use almost fixed resonance components obtained by its vocal tract.
Automatic recognition of Japanese voiceless fricative consonants [s], [&Imoust;] and [h] is discussed terms of acoustic measurements, and an effective algorithm for the recognition is presented. First, discrimination of voiceless fricatives from other phoneme groups, in particular voiceless stops and affricates, is investigated. It is shown that the voiceless fricatives in isolated CV's can be separated from the stops and affricates by the rising patterns of the second and third local peak amplitudes and voiceless interval length. Next, classification within the voiceless fricatives is investigated using power spectral parameters obtained from isolated CV's uttered by five speakers. Effective parameters are the frequency of the center of gravity of the power spectrum, the second local valley frequency, and the first and second local peak frequencies. Based on their distributions, a classification algorithm is constructed and its feasibility is confirmed by recognition experiments. Voiceless fricatives in CV's and VCV's uttered by three speakers chosen from the five speakers used for training are correctly recognized at rates higher than 95%. Also, those uttered by four unknown speakers are recognized with no deterioration.
In case of construction of complex amplitude acoustical holograms, intensity of diffracted wave and spatial frequency distribution on the observing plane which are caused by an arbitrary aperture are not presumed conventionally. If the diffraction patterns (intensity and spatial frequency distributions) of the diffracted waves can be assumed, them the hologram area and sampling intervals are automatically decided. To resolving the problem, a paraxial ray approximated equation is introduced, which indicates relationship between diffraction pattern due to an arbitrary aperture and that due to a model aperture in the Fresnel region, and preliminally calculated Fresnel diffraction patterns due to a model aperture are plotted on graphs. Using these graphs, diffraction patterns on the observing plane due to an arbitrary width aperture are conveniently obtained, so the requested hologram area and the sampling intervals are easily decided using a parameter 'm' (a ratio of (model aperture width/arbitrary aperture width)). These results are useful especially for long wave holography, such as underground, underwater and in air circumstance investigations, architectural acoustics and spatial filtering technologies.
Survey of personal noise exposure due to the activities in the daily lives of 211 subjects was done. The average noise exposure pattern through 24 hours consists of fort main parts- the active daytime corresponding to a high flat level, the hours of sleep corresponding to a low flat level, the time from getting up to going to workplaces in the morning when the level rises up rapidly, and the time staying at home from evening to night until sleep when the level falls down gradually. The difference of properties of noise exposure patterns on occupations is also discussed. The maximum level of personal noise exposure pattern in a day is usually appeared in the activities such as working and commuting for workers, and is appeared mainly in the activities such as shopping, cleaning and social associations for housewives. And the maximum level is highly correlative with L_<eq24>. Then noise exposure in a day is shown to be dominant for time interval about five to seven hours in which L_<eq1/6> ' L_<eq24>. As a measure of uniformity of noise exposure in a day, the entropy of noise exposure pattern is defined and its properties are discussed.
An acoustic radiation system like a loudspeaker can be thought as a linear time invariant system. In this paper, it is tried to express the impulse response mathematically. It is generally difficult to find out analytically the impulse response of such system, but it is very significant to get the mathematical expression of the system characteristics. Accordingly, a mathematical expression of the impulse response of the acoustic radiation system is introduced as a sum of many decayed sine waves which have different frequencies, phases, amplitudes decay factors and time delays, respectively. In order to determine the values of these five kinds of unknown parameters, a nonlinear optimization method is used. At first, the impulse response is practically measured, then each optimum value of unknown parameters of the synthesized impulse response is looked for by means of the Hooke-Jeeves' method. These optimum values can be obtained when the mean square error between the synthesized and measured waveform becomes minimum. As a result of an experiment about edge-clamped circular p;ate radiator with baffle board, the impulse response of the system can be expressed mathematically by a sum of fourteen decayed sine waves. In this case, the error factor indicating the degree of agreement between the synthesized waveform and measured one shows the value of 1. 25%. For an applied example, it is shown that the pole-zero configuration of system can be obtained from the mathematical expression of the impulse response.