Filter Point by point

[ThanhDong]

Dear Sir Henrik_Volkers,

Thank you very much.

I have this question because I see that If I use 1Hz sampling rate and cutoff frequency 0.015Hz for the Butterworth filter (PtbyPt), the output is the same as that of the normal Butterworth filter (fs = 1000Hz and fc = 10Hz).

I really want to know clearly about this digital signal processing. I see that at each time = k/fs (k = 0, 1, ...N-1 and fs = sampling rate) the FOR LOOP will implement one calculation/loop --> the filter (Pt by Pt) must be 1Hz at k/fs with fc = 0.015Hz. Otherwise, we consider a digital array of the input with 1000Hz sampling rate --> the normal Butterworth has fs = 1000Hz and it of course has 10Hz cuttoff frequency. In two cases the fc/fs is the same.

Thanks.

Dong

[Henrik_Volkers]

See, you have the same array of numerical values, and apply the same numerical filter kernel ...(determend by fc/fs, look up digital filter design 🙂 )

but why that is of any importance? Usually you have to deal with real word data 😄

[ThanhDong]

Dear Mr Henrik_Volkers,

When I present or explain to other people, should I say that the fc/fs is the important coefficient (=0.01)? The real sampling rate of 1000Hz and the cutoff frequency of 10Hz of the filter are that of the signals? 

Thanks

Dong

[Henrik_Volkers]

You should only present and explain things you have understood ... if you don't want to blame yourself 😄

To your question:fc/fs can be one (beside others) coefficient that is important for certain tasks...

al lot of other  boundary conditions.  .. definitions ...  have to be regarded... mostly taken for grand ..

And a forum can help with some details ... but the basics are best learned by a structured lecture/book/seminar....   depending on prior knowledge, may take more or less time ...

and need motivated wett cells between your ears 😉  

in your case: numeric signal processing

[ThanhDong]

Dear Mr Henrik_Volkers,

Thank you very much for your recommends. 

I am happy to see your guides .

Dong