5th-order Bessel filter

Bessel filters have a fairly constant transit time (delay) over the pass band and their characteristic thus shows no ringing. This means, however, that the characteristic starts falling off much earlier than in, say, a Butterworth sectton. Also, it takes much langer for the slope of the characteristic to reach the theoretical value of 30 dB/octave; in a Butterworth filter this occurs almost immediately after the cut-off point.