Noise test codes for ITE (information technology equipment), ISO 7779 and ECMA-74 specify, in their informative annex D, two metrics for prominent discrete tones; tone-to-noise ratio and prominence ratio. Both of these metrics have a basic assumption so that the noise emission of question is stationary and can be characterized by only single time-averaged spectrum during the operation of interest. However, some real noise emissions of ITE occasionally are apparently non-stationary, and raise some related issues. This paper discusses the possibility to expand the procedures to time-varying noise from ITE.
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