Active Filter: Bessel
(4th order, 24 dB/octave, Lowpass)

R=4.7k-10 kOhm
Ca=0.7298/(2*pi*Fc*R)
Cb=0.6699/(2*pi*Fc*R)
Cc=1.0046/(2*pi*Fc*R)
Cd=0.3872/(2*pi*Fc*R)

Units: R [Ohm], Cx [F], Fc [Hz]