Filter cut-off calculation

I was putting together a circuit from a tutorial for circuit analysis with Altium Designer and it got me thinking on how to calculate a filters cut-off point.

I think I did something like it in physics last year or possibly longer than that.

Hello,


Step 1: Calculate the network transfer function Hs.
Step 2: Replace s with jw to form Hjw.
Step 3: Calculate the amplitude Hampl from Hjw for any w.
Step 4: Calculate the reference gain, for this amp that is gain at DC, Gdc.
Step 5: Equate the constant 1/sqrt(2) to Hampl/Gdc, and solve for w0.
Step 6: Divide w0 by 2pi to get the cutoff frequency.

If you have a low pass or high pass filter you'll have one cutoff frequency to solve for.
If you have a band pass then you'll have to solve for two cutoff frequencies, low and high.