Active Filter: Bessel
(3st order, 18 dB/octave, Lowpass)

R=4.7k-10 kOhm
Ca=0.9548/(2*pi*Fc*R)
Cb=0.4998/(2*pi*Fc*R)
Cc=0.7560/(2*pi*Fc*R)

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