This 4th order Butterworth filter was generated by the Analog Devices Analog Filter Wizard (https://www.analog.com/designtools/en/filterwizard/). It is comprised of two 2nd order low pass Sallen Key filters.
The passband has 20 dB gain, and the cut off frequency is 10 kHz. With -3dB attenuation, this sets the cut off frequency at around 17dB.
The stop band is -40dB down at 40 kHz. Since the gain is 20dB, -40dB puts the stop band at around -20dB.
