### Pi Attenuator ___a___ is attenuation in dB
___Z_in___ is desired input impedance in Ω
___Z_out___ is desired output impedance in Ω
___K = V_I/V_O = 10^a/20___
___L = K² = 10^a/10___
___A = (L+1) / (L−1)___

___R2 = (L−1) / 2·√(Z_in · Z_out / L)___
___R1 = 1 / (A/Z_in − 1/R2)___
___R3 = 1 / (A/Z_out − 1/R2)___