# 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.

In the frequency range in which the filter amplitude characteristics remain flat, the phase shift Φ of a Butterworth filter can be approximated by
Φ = 81 x (f/f0) degrees for second order
Φ = 150 x (f/f0) degrees for fourth order
Φ = 294 x (f/f0) degrees for eighth order
The time delay for all filter orders is: t = (Φ/360) x (1/f0)

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Source: https://www.legislation.gov.uk/eur/2009/631/annex/part/III/division/appendix+ii/division/2/division/2.3/division/1 (the official version)
Page: https://openlegislation.uk/eu-regulation-2009-631/annex/part-III/division-appendix+ii/division-2/division-2.3/division-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.