, ▁" b ass ", ▁" tre ble " ▁and ▁" volume " ▁controls ▁on ▁s tere os , ▁and ▁" t int " ▁controls ▁on ▁TV s . ▁Common ▁analog ▁processing ▁elements ▁include ▁capac itors , ▁resist ors ▁and ▁induct ors ▁( as ▁the ▁pass ive ▁elements ) ▁and ▁trans ist ors ▁or ▁op amps ▁( as ▁the ▁active ▁elements ). ▁ ▁Tools ▁used ▁in ▁analog ▁signal ▁processing ▁A ▁system ' s ▁behavior ▁can ▁be ▁mathemat ically ▁mode led ▁and ▁is ▁represented ▁in ▁the ▁time ▁domain ▁as ▁h ( t ) ▁and ▁in ▁the ▁frequency ▁domain ▁as ▁H ( s ), ▁where ▁s ▁is ▁a ▁complex ▁number ▁in ▁the ▁form ▁of ▁s = a + ib , ▁or ▁s = a + jb ▁in ▁elect rical ▁engineering ▁terms ▁( elect rical ▁engine ers ▁use ▁" j " ▁instead ▁of ▁" i " ▁because ▁current ▁is ▁represented ▁by ▁the ▁variable ▁i ). ▁ ▁Input ▁signals ▁are ▁usually ▁called ▁x ( t ) ▁or ▁X ( s ) ▁and ▁output ▁signals ▁are ▁usually ▁called ▁y ( t ) ▁or ▁Y ( s ). ▁ ▁Con volution ▁Con volution ▁is ▁the ▁basic ▁concept ▁in ▁signal ▁processing ▁that ▁states ▁an ▁input ▁signal ▁can ▁be ▁combined ▁with ▁the ▁system ' s ▁function ▁to ▁find ▁the ▁output ▁signal . ▁It ▁is ▁the ▁integral ▁of ▁the ▁product ▁of ▁two ▁wave forms ▁after ▁one ▁has ▁revers ed ▁and ▁shift ed ; ▁the ▁symbol ▁for ▁convolution ▁is ▁*. ▁▁▁▁ ▁That ▁is ▁the ▁convolution ▁integral ▁and ▁is ▁used ▁to ▁find ▁the ▁convolution