When you need to design a frequency filter, first you must know its purpose. Then you can plan the frequencies it passes and if any ripple or sagging is tolerable, and how much attenuation it must provide at certain frequencies.
With the info about how the filter must perform you can design it using R and C values and ratios and how much gain is its opamp. You can select how many orders it needs.
With the info about how the filter must perform you can design it using R and C values and ratios and how much gain is its opamp. You can select how many orders it needs.