his is where Bode plots and asymptotes come in. Your example would (assuming second order filters) result in a filter with a cutoff at 10 kHz with 40 dB/dec roll off, the roll off increasing to 80 dB/dec at 50 kHz.
So if I want a better roll-off isn't better to use the same fc? So I get 80 db/dec roll off?
Or are there any advantages or reasons to use different fc?
I'm suspicious of your Sallen-Key filter, R3 seems way too high. Shouldn't it be 100 ohms?
I'm using the values that are on the actual circuit, I have an old post that I explain a little how I got to this circuit.
Not sure if the author was knowing what they were doing, because there are a lot of mistakes on the circuit, as resistors and capacitors grounded on both pins.
There are capacitors on the output of each opamp going to ground, which for me is weird since it decreases the slew-rate of the opamp. Not sure if there any motive to use capacitors like that on the output of the opamps.
I will post the whole circuit some time, it's just that I'm taking it by parts to focus and learn in depth about it and electronic in general.