騒音・振動計測における計器特性と確率評価の基本的関係

抄録

First, it is theoretically considered how the fundamental mechanism of mean squaring operation of sound level or vibration level meters affects the probability distribution forms of output sound or vibration level in direct connection with the stochastic evaluation. The effect of time constant and frequency characteristic of the indicating system is reflected in the parameters of output probability distribution together with an amplitude-frequency spectrum of input noise or vibration. More explicitly, two modes of statistical approach to the above problem are given : In the first approach, some basic properties which are manifested throughout the entire random variations (e. g. , a boundary amplitude region where the output fluctuation of mean squaring circuit takes such as (- ∞, +∞), (-∞, 0), or (0, +∞)). are considered. Then, the probability distribution of output is obtained in the form of an orthonormal expansion, each coefficient of which may be expressed as function of value, variance, highorder moments, etc. reflecting the internal mechanism of indicating system. The second recti approach is in rather striking contrast to the first approach and the nonlinear operation itself is the first principal consideration in it. The response of the indicating system to a random input is analyzed in the same way as when the input signal is deterministic and then the probability distribution of random signal is taken into consideration. The theoretically derived output level distributions are able to be expressed only with informations on a time constant of the indicating system and amplitude-frequency spectrum of random input and/or indicating system and they are in good agreement with experimentally sampled values. Especially it must be noticed that an information on phase-frequency spectrum is completely unnecessary.