▁intensity ▁of ▁pe aks ▁on ▁the ▁aut oc or relation ▁spectrum ▁are ▁directly ▁proportional ▁to ▁the ▁relative ▁importance ▁of ▁the ▁intensity ▁change ▁in ▁the ▁original ▁spect ra . ▁Hence , ▁if ▁an ▁inten se ▁band ▁is ▁present ▁at ▁position ▁x , ▁it ▁is ▁very ▁likely ▁that ▁a ▁true ▁intensity ▁change ▁is ▁occurr ing ▁and ▁the ▁peak ▁is ▁not ▁due ▁to ▁noise . ▁ ▁Add itional ▁techniques ▁help ▁to ▁filter ▁the ▁pe aks ▁that ▁can ▁be ▁seen ▁in ▁the ▁ 2 D ▁synchron ous ▁and ▁asynchronous ▁spect ra . ▁ ▁Det erm ining ▁the ▁direction ▁of ▁intensity ▁change ▁It ▁is ▁not ▁always ▁possible ▁to ▁une qu iv oc ally ▁determine ▁the ▁direction ▁of ▁intensity ▁change , ▁such ▁as ▁is ▁for ▁example ▁the ▁case ▁for ▁highly ▁over la pping ▁signals ▁next ▁to ▁each ▁other ▁and ▁of ▁which ▁the ▁intensity ▁changes ▁in ▁the ▁opposite ▁direction . ▁This ▁is ▁where ▁the ▁off ▁diagonal ▁pe aks ▁in ▁the ▁synchron ous ▁ 2 D ▁spectrum ▁are ▁used ▁for : ▁ ▁if ▁there ▁is ▁a ▁positive ▁cross - pe ak ▁at ▁( x , ▁y ) ▁in ▁the ▁synchron ous ▁ 2 D ▁spectrum , ▁the ▁intensity ▁of ▁the ▁signals ▁at ▁x ▁and ▁y ▁changes ▁in ▁the ▁same ▁direction ▁if ▁there ▁is ▁a ▁negative ▁cross - pe ak ▁at ▁( x , ▁y ) ▁in ▁the ▁synchron ous ▁ 2 D ▁spectrum , ▁the ▁intensity ▁of ▁the ▁signals ▁at ▁x ▁and ▁y ▁changes ▁in ▁the ▁opposite ▁direction ▁ ▁As ▁can ▁be ▁seen ▁in ▁the ▁ 2 D ▁synchron ous ▁spectrum