The noise equivalent bandwidth (or equivalent noise bandwidth (enbw)) of a system of frequency response H ( f ) is the bandwidth of an ideal filter with rectangular frequency response centered on the system's central frequency that produces the same average power outgoing H ( f ) when both systems are excited with a white noise source. The value of the noise equivalent bandwidth depends on the ideal filter reference gain used. Typically, this gain equals | H ( f ) | at its center frequency, but it can also equal the peak value of | H ( f ) | .