Archives of Acoustics, 27, 3, pp. , 2002

A stochastic evaluation for non-stationary random noise over a long time period based on local statinarity and its application to actual acoustics environment

K. Nashimura
Faculty of Engineering, Kinki University

M. Ohta
The Emeritus Professor of Hiroshima University

A non-stationary environmental noise fluctuations can be
treated as some composition of local state strips having arbitrary fluctuating
pattern in a locally stationary time period. Its non-stationary characteristics
can be seen in the form of its changing stage from a locally stationary state to
another one by means of its temporal change of probability distribution. For a
non-stationarity with continuously slow temporal change, the noise evaluation
method is derived by considering the temporal change of moment statistics or
distribution parameters. On the other hand, for a non-stationarity with stepwise
rapid variation like an ON/OFF operation of machine, the noise evaluation method
is derived by considering in principle the occurring probability of each of
locally stationary state based on the mutually exclusive property. In the
experimental consideration, the above contrastive two evaluation methods have
been applied to actual cases with slowly changing environmental noise and
rapidly changing machine noise.
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