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Below the green plot Vin is 5Hz sine voltage signal from a function generator output sampled at 12kHz sampling rate:

enter image description here

The blue plot Vout is the processed/filtered data by using the following code in Python:

#Transfer function
fc = 1 # roll off freq
wc = 2*numpy.pi*fc 
sys = signal.lti([1], [1/wc, 1])  # transfer function

#Output in time (Response of the filter to the input)
tout, v_out, x = signal.lsim(sys, v_in, time)  # output

And here is Vout in a more detailed view:

enter image description here

Basically I define a low pass filter transfer function using: sys = signal.lti([ 1 ], [1/wc, 1]).

Then the Vout is obtained from tout, v_out, x = signal.lsim(sys, v_in, time)

So Vout is the filtered response of Vin.

If you compare the Vin and Vout in above plots, Vout looks like it is processed like in Laplace domain, that is to say Vout looks like it is both the transient and steady state response of Vin.

(This problem seen more obvious for a DC input; the output Vout becomes like a transient response of an RC filter)

Having the sampled data like in green plot Vin, how can we obtain a steady sate response of such filter? Or at least close to steady state.

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