▁a ▁signal ▁that ▁has ▁an ▁infinite ▁magnitude ▁and ▁an ▁inf init es im ally ▁narrow ▁width ▁with ▁an ▁area ▁under ▁it ▁of ▁one , ▁centered ▁at ▁zero . ▁ ▁An ▁imp ulse ▁can ▁be ▁represented ▁as ▁an ▁infinite ▁sum ▁of ▁sin us oid s ▁that ▁includes ▁all ▁possible ▁frequencies . ▁ ▁It ▁is ▁not , ▁in ▁reality , ▁possible ▁to ▁generate ▁such ▁a ▁signal , ▁but ▁it ▁can ▁be ▁sufficiently ▁approxim ated ▁with ▁a ▁large ▁amplitude , ▁narrow ▁pul se , ▁to ▁produce ▁the ▁theoretical ▁imp ulse ▁response ▁in ▁a ▁network ▁to ▁a ▁high ▁degree ▁of ▁accuracy . ▁ ▁The ▁symbol ▁for ▁an ▁imp ulse ▁is ▁ δ ( t ). ▁ ▁If ▁an ▁imp ulse ▁is ▁used ▁as ▁an ▁input ▁to ▁a ▁system , ▁the ▁output ▁is ▁known ▁as ▁the ▁imp ulse ▁response . ▁ ▁The ▁imp ulse ▁response ▁defines ▁the ▁system ▁because ▁all ▁possible ▁frequencies ▁are ▁represented ▁in ▁the ▁input ▁ ▁Step ▁A ▁unit ▁step ▁function , ▁also ▁called ▁the ▁He av is ide ▁step ▁function , ▁is ▁a ▁signal ▁that ▁has ▁a ▁magnitude ▁of ▁zero ▁before ▁zero ▁and ▁a ▁magnitude ▁of ▁one ▁after ▁zero . ▁ ▁The ▁symbol ▁for ▁a ▁unit ▁step ▁is ▁u ( t ). ▁ ▁If ▁a ▁step ▁is ▁used ▁as ▁the ▁input ▁to ▁a ▁system , ▁the ▁output ▁is ▁called ▁the ▁step ▁response . ▁ ▁The ▁step ▁response ▁shows ▁how ▁a ▁system ▁respond s ▁to ▁a ▁sudden ▁input , ▁similar ▁to ▁turning ▁on ▁a ▁switch . ▁ ▁The ▁period ▁before ▁the ▁output ▁stabil izes ▁is ▁called