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Explanation for the Lowpass filter

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patan.gova

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Hello,
I have a signal as shown here **broken link removed**
and I want to design a lowpass filter in matlab.But for this I need to select the frequency part parameters like Fpass,Fstop,Fs and for magnitude need to slect the Apss and Astop.
From the signal above shown I am clear with selction of Fs should be >10Hz.But I am confused with Apass,Astop,Fstop,Fpass.
Can someone how they need to be selected to get a cutoff freq of 3Hz I mean how the value(increase or decrease) effect on the filter design and on the output(filtered) signal.
I tried designing a lowpass as shown LPfilter.jpg but I wondering what are these in the red marked region of image.
The actual LP filter should look like this https://upload.wikimedia.org/wikipedia/commons/6/60/Butterworth_response.svg what is the difference of one desinged and one in wiki in both.
Can anyone expalin about this.
Thanks.
 

LvW

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The lowpass as referenced by you (wikimedia) is of FIRST order with a slope of -20 dB/dec.
The question you have to answer is: Does such a simple lowpass fulfill your attenuation requirements?
A lowpass has the task to let path the desired signal and to attenuate unwanted frequency components - and that is the meaning of the parameters Fpass,Fstop,Fs, Apss and Astop.
(Frequencies F and the associated minimum damping requirements).
 

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