Many objective characteristics of loudspeakers are measured in factories and laboratories, but there is little knowledge about how they affect sound quality. It is necessary to reveal the relation between objective characteristics and sound quality in order to improve sound quality of loudspeakers. In this paper, the relation between subjective evaluation of sound quality and objective data to reveal the characteristics which influence sound quality to a great extent is investigated. In the subjective listening tests, preference judgments which were subjected to factor analysis, similarity judgments which were subjected to multidimensional scaling and verbal descriptions of sound quality were carried out. The factor analysis of preference data yielded a preference space of three factors (Fig. 5). The first of them is the "consensus preference" factor and the remaining two are the "individual difference" factors. As a result of multidimensional scaling, similarity data are summed up in three psychological dimensions (Fig. 7). Interpretation of these dimensions indicates that they represent "volume and extent", "brightness" and "beauty" respectively (Fig. 7). The relation between objective data and subjective data was analyzed in two respects. Firstly, measured data sixteen objective characteristics were rated from the view point of high fidelity reproduction (Table 3). These characteristics were fitted into the preference space as vectors (Fig. 14). Rating scores of sound pressure responses measured in a listening room and an anechoic room have a high correlation with the "consensus preference" factor. Secondly, similarity of response patterns among loudspeakers was calculated for each objective characteristic and it was subjected to multidimensional scaling. The configurations of loudspeakers based on objective similarity were compared with the ones based on subjective similarity (Fig. 16). Similarity of sound pressure response in the listening room has a close coincidence with subjective similarity. These results imply the necessity of measurements not only in an anechoic room but also in a listening room.
A new method of analyzing the stereophonic sound field has been developed. The characteristic function of this analyzing method is the possibility both to evaluate the quality of a sound image and to calculate its direction, by paying attention to the relation between the amplitude ratio (ΔP) and the phase difference (Δφ) of the signals at the entrance of the external auditory canals of both ears of a listener (See Fig. 3, 4, 5, 6 and Eq. 1, 2, 3, 4). Fig. 4 shows the relation between ΔP and Δφ represented on the ΔP-Δφ plane when a real sound source (f=500 Hz) moves along the circumference of a listener. The representational relation of amplitude ratio and phase difference between two loudspeakers and both ears is shown in Fig. 6, obtained by Eq. 1, 2, 3, 4. The propriety of this analyzing method is discussed by experiments of subjective evaluation. Results of the subjective evaluation of sound image quality and the sound image direction are shown in Table 1, Table 2 respectively, which show no clear tendency of the sound image quality and sound image direction. The ΔP-Δφ analysis, however, can obtain clear tendency shown in Fig. 9 and Fig. 10. As the first example of application of this analyzing method, the "180゜natural sound image calizer" has been developed by which a natural sound image can be obtained outside of two long speakers (See Fig. 13, 14, 15, 16). As the second example of application, the conventional methods of using microphone systems so as the MS microphone system, the spaced mecrophone and the dummy-head system, are analysis in quality and direction of a sound image, for which it can be said that the conventional method of using microphone systems is proper (See Fig. 17, 18, 19, 20, 21, 22, 23)
We can perceive the subjective tempo of a periodical burst signal train. With the Japanese language which involves a weak stress accent and relatively monotonical disposition of the syllables, the tempo sensation has a close relation with the speech quality. But it is not clear how the tempo sensation is affected by the physical characteristics of the signal, and which position of the signal wave corresponds to the tempo sensation. To answer these questions, we executed some phychological experiments on the tempo sensation using burst noise. The first experiment is concerned with subjective perception of the interrupted signal. As the pause time is increased, we can clearly perceive three sensation regions, i. e. continuous, ripply, and discrete sensation. These phenomena are due to the integral characteristics of the hearing mechanism. Using a psychological test procedure, the critical pause times corresponding to the boundary of the above sensation regions are examined. As the results, the critcal pause time change from the continuous to the ripply region is about 4 msec-6msec, and from the ripply to the discrete region is about 30 msec. Then it is examined how the tempo sesation affected by the difference of period, sound of timbre and duration of the burst signal. It is that only the effect of duration difference is highly significant. Holding the physical period of the signal constant, the subjective tempo is perceived faster as the duty cycle of the burst signal increase. This relaiton is shown in Fig. 8. The abscissa is the duty cycle and the ordinate is thepercent cycle of the period neccessary to match the same tempo sensation. Thirdly it is discussed, which position of the signal wave corresponds to the tempo sensation. As for the same form is repeated, we cannot obtain information in regard to the position on the same form. So, in this experiment, the burst signal constructed of rectangular and triangular waves the subject adjust the relative position to obtain uniform tempo sensation. As the result, it is formed that the corresponding position is neither the front nor the energy center of the signal, exists in an intermediate position between then
Everybody knows that one will suddenly fall into misjudgment in sequential item recognition, when the sequence such as music or speech comes at a too rapid rate. The author named the threshold of such rate the "critical rate for identification(C. R. I. ). , and studied several factors which affect the critical rate, by means of Warren-type experiments. The results show that kind of sound, number of classifying categories, silent interval between items, and similarity between sequential items each affect the C. R. I. . On the basis of the results, the relations between auditory fusion and auditory stream segregation and the C. R. I. are discussed, and auditory information processing rates are estimated from these C. R. I data.