I have connected 3 filters in series using the cascade command. The 1st filter decimate by R while the 2nd and the 3rd by two. Which sampling frequency should I use to convert the x-axis scale from normalized frequency to absolute frequency?

Fs = 2.3*(53.10348e6); R256 = 256; D = 1; Nsec = 5; Fpass = 5e3; % Passband Frequency Fstop = 15e3;

h = fdesign.decimator(R256, 'CIC', D, 'Fp,Ast', Fpass, Astop, Fs); HCIC256 = design(h, 'multisection');

set(HCIC256, 'Arithmetic', 'fixed', ... 'InputWordLength', 16, ... 'InputFracLength', 15, ... 'NumberofSection', Nsec,... 'FilterInternals', 'MinWordLengths',... 'OutputWordLength', 24);

gainHCIC256 = gain(HCIC256); HCIC256Comp = cascade(dfilt.scalar(1/gain(HCIC256)),HCIC256);

hcomp256 = fdesign.decimator(2, 'CIC Compensator', D, Nsec, 'n,fp,fst', ... N43, Fpass, Fstop, Fs/R256);

Hdcomp256 = design(hcomp256, 'equiripple', ... 'StopbandShape', 'flat');

set(Hdcomp256, 'Arithmetic', 'fixed', ... 'InputWordLength', 24, ... 'InputFracLength', -17, ... 'CoeffWordLength', 12, ... 'CoeffAutoScale', true, ... 'FilterInternals', 'SpecifyPrecision',... 'OutputWordLength', 24,... 'OutputFracLength', -17);

HCCIC256 = cascade(Hdcomp256,HCIC256Comp);

hfirdec23 = fdesign.decimator(2, 'Lowpass', 'n,fp,fst', N23, Fpass,... FstopFIR, Fs/(R256*2));

Hfirdec23 = design(hfirdec23, 'equiripple', ... 'StopbandShape', 'flat');

set(Hfirdec23, 'Arithmetic', 'fixed', ... 'InputWordLength', 24, ... 'InputFracLength', -14, ... 'CoeffWordLength', 12, ... 'CoeffAutoScale', true, ... 'FilterInternals', 'SpecifyPrecision',... 'OutputWordLength', 32,... 'OutputFracLength', -17);

Hd23 = cascade(Hfirdec23,HCCIC256);