You do not want pass band attenuation.
Instead you want frequencies below 3kHz and above 20kHz to be attenuated at 80db/decade which is 24db/octave which are forth-order Butterworth filters.
You do not want pass band attenuation.
Instead you want frequencies below 3kHz and above 20kHz to be attenuated at 80db/decade which is 24db/octave which are forth-order Butterworth filters.