Recognition of tonal components
Extract from Ministerial Decree 16-03-98 Annex B Paragraph 10
Recognition of tonal components of noise
To identify the presence of Tonal Components (TC) in the noise, a spectral analysis is performed for normalized 1/3 octave bands. Only TCs that are stationary in time and frequency are considered. If sequential filters are used, the minimum of each band with a Fast time constant is determined. If parallel filters are used, the level of the stationary spectrum is highlighted by the minimum level in each band. To highlight TCs that are at the crossover frequency of two 1/3 octave filters, filters with greater selective power or alternative crossover frequencies can be used.
The analysis must be carried out in the frequency range between 20 Hz and 20 kHz. A TC is present if the minimum level of a band exceeds the minimum levels of adjacent bands by at least 5 dB. The correction factor KT as defined in point 15 of Annex A is applied only if the TC touches an isophonic equal to or higher than the highest level reached by the other components of the spectrum. The technical reference standard is ISO 266:1987.
Many years after the entry into force of the Ministerial Decree of 16 March 1998 and with greater experience resulting from the examination of the various critical situations in the application of the criterion for the recognition of tonal components, some useful functions have been added to the NoiseWorks software to provide the expert operator with a more versatile investigation tool for this type of research.