A new model equation of normal impedance is proposed in an attempt to represent much more varieties of the frequency dependance of excess attenuation due to ground. There are measurements of outdoor noise propagation in near-horizontal directions over several ground surfaces and that of noise propagation over a lawn-covered or noncovered, soil in an anechoic room. From a good agreement between the measured results and the calculated one, it is shown that the propagation of noise above ground can be predicted by using the model equation of impedance and the theory of sound propagation above a locally reacting boundary surface with finite impedance.
The effects of noise, distortion and band limitation on the tone quality of broadcasting sounds are investigated using the method of continuous judgment by category. The advantages of this method are that the long-term program can be used as stimulus as it is, and that subjects listen to the program without paying attention to any specific deteriorative conditions. Popular songs with conversation between an announcer and singers broadcasted by NHK FM are used as source program. The duration is about 23 minutes. Four kind of noise, three kinds of distortion and three kinds of band limitation are added on the program. Twenty subjects judge the instantaneous tone quality using eight categories. The effects of the deteriorative conditions are compared with one another in the same context. As a results, it is found that this method is appropriate to evaluate the tone quality of broadcasting sounds in a natural listening attitude. And it is confirmed by the experiment using this method that noise has the greatest effect on the tone quality, and that distortion also plays an important role in the estimation of the tone quality when either noise or band limitation is not added.