Inthispaperageneraltheoryofmultistagedecimatorsandinterpolatorsforsamplingratereductionandsamplingrateincreaseispresented.Asetofcurvesandthenecessaryrelationsforoptimallydesigningmultistagedecimatorsisalsogiven.Itisshownthattheprocessesofdecimationandinterpolationaredualsandtherefore