In order to make it clear what kind of physical characteristics mimic voices of a talking bird mynah has, 111 mimic of a well-trained mynah are analyzed in (1) the intensity pattern of sound wave form, (2) the fundamental frequency contour, (3) the long term spectrum, (4) the spectral envelope peaks of vowels, (5) the time spectral pattern of consonants. And they are compared with those of tutor's voices. (1) Though the intensity patterns of mimic voices are a little bit different from the tutor's, the duration of the pause in the speech sound and the duration of the burst in some stop consonants are very similar to those of tutor's voices. (2) The fundamental frequency contour shows generally good coincidence between them. The fluctuations of fundamental frequency are also found in mimic voices, however, they are comparatively larger than those of tutor's voices. (3) The long term spectrum of mimic vices has a peak around 900 Hz and the slope for the lower frequency part is 2 dB/oct. and -10dB/oct. for higher frequency part. So, the spectral components below 500 Hz are smaller than those of 1 to 3 kHz by 3 to 10dB. (4) As to the first spectral envelope peaks (P_1) appear around 1kHz in every vowel, it seems very hard to categorize five vowels on the P_1-P_2 plane. (5) As to the spectral changes, the transition of the spectral envelope peaks in the range of 1 to 3kHz are found similar to the tutor's though that of P_1 is not so clear. These physical characteristics of mimic voices of mynah bird are supposed to depend not only on its vocalization but also its auditory function, so that some suggestions will be obtained for the studies of speech synthesis and automatic speech recognition. However, some questions still remain as to how mimic voices with different spectral pattern are processed in the human auditory system.
An experimental study was made of the air flow noise generated by a nozzle with a sudden enlargement in the cross-section. Such nozzle shows a characteristic phenomenon that the A-weighted sound pressure level takes a minimum at a specified pressure of supplied air and generates a high intensity noise with a high frequency, screech noise, around the pressure. The screech noise gives a significant displeasure to a person handling the nozzle. The purpose of the study is to develop the preventive method against screech noise by air flow control, since the noise is closely related to the flow condition through the nozzle. It was found that the effective method was to protrude the nozzle into an enlarged region, or to make small holes in the wall of the region. The mechanism of the noise generation was also investigated and a design chart was prepared for the optimum nozzle geometry for the noise reduction.
The well-known equivalent sound level (L_<Aeq>, abbr. , L_<eq>) adopted for a unified acoustic description of environmental noise by ISO 1996 has now gained some widespread acceptance, for example, as a measure of sound exposure. Nevertheless, in a theoretical study of L_<eq> statistics, considerable efforts must be yet spent for establishing the effective measurement procedure of L_<eq>, especially from the methodological point of view. This paper discusses the effect of the sampling period, Δ, and the sample number, N, on the L_<eq> statistics in a constant measurement time, T(=NΔ). The theoretical probability expression of general series expansion type for the average energy, E(L_<eq>=10log E/E_0, E_0=10^<-12>W/m^2), proposed here has a gamma distribution as its first expansion term and also reflects various types of linear and/or nonlinear (multi-dimensional) correlation properties for the sound power fluctuation wave into its each expansion terms. Theoretical and experimental results demonstrate the fact that a fluctuation probability distribution form of L_<eq> converges to a certain proper probability form with non-zero variance, even when N tends to infinity as Δ approaches smaller than a Nyquist period (1/2W, W: equivalent frequency bandwidth of sound power fluctuation) under the condition of a constant T. The effectiveness of the proposed theory has been confirmed experimentally too by applying it to the actual traffic noise data observed at the central area of large city.
Survey of daily noise exposure of 315 residences in Nagoya City was made in the last half period of 1982. The equivalent sound levels measured nearby houses during 24 hours are analyzed by using quantification theory type I. The results are summarized as follows. 1) The prominent factors for noise exposure of residence in urban area are road and land use as easily expected. 2) The effects of factory and train for noise exposure are noise exposure are noticed in daytime and in the other time respectively. 3) The effects of season (i. e. month) and type of house evident in residual neise level, L^<90>_<eq1/6>. 4) Reduction of noise exposure by neighboring buildings as well as fence of residence is also confirmed. Based on these results we have shown that classification of urban area by land use and road is very useful for discussing environmental noise. If is interesting to know that the above classification is just corresponding to districts which has being employed to define standard values of environmental noise in our country.