# Commission Regulation (EC) No 631/2009 of 22 July 2009 laying down detailed rules for the implementation of Annex I to Regulation (EC) No 78/2009 of the European Parliament and of the Council on the type-approval of motor vehicles with regard to the protection of pedestrians and other vulnerable road users, amending Directive 2007/46/EC and repealing Directives 2003/102/EC and 2005/66/EC, Division: Note:

Extent: E+W+S+N.I.

For a Butterworth filter the attenuation is given by:
A 2 = 1 1 + f max / f 0 2n and A 2 = 1 1 + f N / f 0 2n where:
n is the filter order
fmax is the relevant frequency range (30 Hz)
fo is the filter cut-off frequency
fN is the Nyquist or cut-off frequency.
For a fourth order filter
for A = 0,9995:
fo = 2,37 × fmax
for A = 0,0005:
fS, = 2 × (6,69 × fo), where fS, is the sampling frequency = 2 × fN.

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Source: https://www.legislation.gov.uk/eur/2009/631/annex/part/III/division/appendix+ii/division/2/division/2.2/division/1 (the official version)
Page: https://openlegislation.uk/eu-regulation-2009-631/annex/part-III/division-appendix+ii/division-2/division-2.2/division-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.