Now you all know the various analog filter types,Butterworth,Bessel,Chebychev...

My question is,if I put single capacitor in the signal path,it will block dc,acting like highpass filter,I believe its 6db per octave roll off.What type of filter that is? I want to imagine what kind of time domain transient response will it have,Bessel filter have less overshoot and post ringing than Butterworth,and I have no idea if my series capacitor is butterworth or bessel or maybe something else.

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    \$\begingroup\$ Capacitor in series is single-pole high-pass RC filter. (Well, there's some resistance to ground somewhere, which provides the R.) \$\endgroup\$ – Nick Alexeev Apr 21 '17 at 2:02
  • \$\begingroup\$ Who gave me the dislike and why? :( So as I understand it," single pole" is specific type of filter just like Butterworth or Bessel with its own unique transition band and impulse shape \$\endgroup\$ – wav scientist Apr 21 '17 at 3:20
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    \$\begingroup\$ A single-pole filter is a single-pole filter, period. Butterworth, Bessel, Cheybyshev, etc, filters require multiple poles. \$\endgroup\$ – user207421 Apr 21 '17 at 4:57

A single-capacitor filter, with an R, has too few degrees-of-freedom in the pulse response; basically, you have NO ADJUSTMENTS POSSIBLE. Only the F3dB is adjustable. Overshoot does not occur, so cannot be adjusted.

EDIT The shape of the magnitude response of lowpass RC filter can only be

$$1 / sqrt[ 1 + (Freq/Freq_3dB)^2]$$

Here are mag/phase for 0.1 to 10Hz, 10Hz to 1KHz, 1KHz to 100KHz. Notice the phase shows a useful change per decade. enter image description here

Above F3dB, that same deltaPhase occurs, as phaseshift approaches 90 degrees.

  • \$\begingroup\$ That means single pole filter is unique specific type of filter different from Bessel or Butterworth? If I say "single pole" to some experiences ee guy,will he know that its different thing that bessel or butterworth? Since it doesnt have ripple in passband or stopband I assumed it must one of the two,that assumption was wrong and single pole have different roll off shape and phase/transient response than the above mentioned filters,correct? \$\endgroup\$ – wav scientist Apr 21 '17 at 3:34
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    \$\begingroup\$ You are correct. Single pole must have 1/sqrt[1 +(F/Fc)^2 ] rolloff of its magnitude. You can make no adjustments to the shape of the rolloff. \$\endgroup\$ – analogsystemsrf Apr 21 '17 at 3:39

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