1                          
                         fo = -------   ( R = R1 = R2,  R3 = R/2,  C = C1 = C2, C3 = 2C )
                                  2πRC                      

                            
                    대역리젝션필터(BRF), 대역트랩필터(BTF)혹은 노치(Notch)

                    필터라고도 한다.