音の立上がり時間と大きさについて : エネルギー値との関係 (&lt特集&gt聴覚)

抄録

In order to understand the temporal characteristics of hearing, it is quite important to investigate the effects of various temporal factors of stimuli. We may mention 'rise time of stimuli' as one of the factors. Several experiments have been conducted concerning the effects of rise time on the loudness, but the results have not always been conclusive. Our previous experiments concerning level-fluctuating noises show that loudness is determined by the energy which the noises have. Therefore it will be necessary also to investigate the effect of rise time in respect of energy. So, in this experiment we investigate the effect of rise time on the loudness using such stimuli as shown in Fig. 1-c. As a stimulus white noise is used and it is presented monaurally to subjects, seated alone in the sound-proof room. All conditions of stimuli-intensity, duration, rise time and stimulus interval-are automatically controlled and presented by Programmable Sound Control System (abbreviated as PSCS), which has been developed in our laboratory. Three levels of intensity, 60, 75 &amp 90 dB SPL and 3 kinds of rise time, 100, 300 &amp 500 msec are used as standard stimulus (Ss), and as comparison stimulus (Sc) a steady state noise is used which has the same SPL or the same duration as Ss. In Exp. 1 the duration of Sc is held constant and subjects match the loudness of Sc with that of Ss by controlling the SPL of Sc. In Exp. 2 and 3 the SPL of Sc is held constant and the duration is varied by experimenter in Exp. 2 (method of limits) and by subjects themselves in Exp. 3 (method of adjustment). The result shows that in all conditions PSE is in good agreement with Ss when compared after both PSE and Ss are converted into energy. Therefore it may be concluded that the effect of rise time on the loudness is attributable to the change of energy. But there is as invariable, though slight, difference among PSE obtained in Exp. 1, 2 and 3. That is to say, PSE obtained in Exp. 2 and 3 is louder than that in Exp. 1 in all conditions. This may be due to the change of attribute of sensation since the duration of Sc in Exp. 2 and 3 is very short. Supplementary experiment concerning the change of the attribute of sensation of short noises using semantic differential shows that very short noise is judged sharp, though soft. Therefore when the duration of Sc is varied, there is a possibility that the judgment of loudness may be affected by the impression of sharpness, causing the overestimation of Ss in Exp. 2 and 3.