i have a signal now i want to calculate the DC values of it

Suppose i have a signal which has AC and DC commponet.........

now i want to calculate the DC signal from it....

I have done low pass filterting as below

Fs = fs;  % Sampling Frequency

Fpass = 0.8;        % Passband Frequency
Fstop = 1;         % Stopband Frequency
Apass = 1;           % Passband Ripple (dB)
Astop = 80;          % Stopband Attenuation (dB)
match = 'passband';  % Band to match exactly

% Construct an FDESIGN object and call its CHEBY1 method.
h2  = fdesign.lowpass(Fpass, Fstop, Apass, Astop, Fs);
Hd2 = design(h2, 'cheby1', 'MatchExactly', match);

s1_dc = filter (Hd2 , s1);

but still i could not get the required DC signal

what should i do ? do i need to use any other Low pass filter ??

Answer 1

[Honglei Chen]

Theoretically, the DC component is simply

mean(s1)

If this is not what you want, could you elaborate a little more what you mean by DC signal?

[Liaquat Ali]

I have a signal S1 which has low frequency values till 5 Hz.

Now i have a formula which is

R(i) = log10((s1_ac_dc(i))/s1_dc(i)) / log10((s3_ac_dc(i))/s3_dc(i));

Which means i have to divide the signal value with its DC value......

so for a signal S1 i need its DC value at that point.??

[Honglei Chen]

what is the meaning of index i? In general DC value is a constant across the signal