Question about SourceFilter

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dianavertiz
Posts: 4
Joined: 16 May 2021, 19:47

Question about SourceFilter

Post by dianavertiz » 11 Jul 2021, 17:04

Hello,
I'm using SourceFilter in a signal source module implemented for a biopotencial amplifier.
Everything works fine, I can select the frequencies for low-pass, high-pass and notch filters
I save the signals to a .dat file but when I load the data using Matlab, I can see the filters are not working
I can only see the notch effect in the signal spectrum but not the effect from low-pass and high-pass filters.
Any idea why would it be happening?
Thanks!!
Diana

mellinger
Posts: 1173
Joined: 12 Feb 2003, 11:06

Re: Question about SourceFilter

Post by mellinger » 15 Jul 2021, 13:22

Hi,

you need to enable SourceFilter filters in the configuration dialog, under the Source tab. If you enable a filter by right-clicking the source window, the filter will only be applied to the data displayed in the window, not to the data written to disk.

HTH,
Juergen

dianavertiz
Posts: 4
Joined: 16 May 2021, 19:47

Re: Question about SourceFilter

Post by dianavertiz » 21 Jul 2021, 17:43

Thanks for your answer,
I enable filters in the Source tab, in parameter configuration. When I analyze data, written to disk, in matlab I can only see the notch
effect in the signal spectrum. That's why I don't understand why notch filter works and low/high-pass filters don't.
Thanks again
Diana

mellinger
Posts: 1173
Joined: 12 Feb 2003, 11:06

Re: Question about SourceFilter

Post by mellinger » 22 Jul 2021, 10:12

Hi,

I used the SignalGenerator source module to verify that the filters are working. I verified by inspecting the signal in the source window. The high pass filter successfully removed an offset of 50muV. The low pass filter showed a smoothed signal, compared to the raw white noise of 100muV.

The Notch filter is a 3rd order Chebycheff filter, whereas low and high pass are of order 1 and thus fall off only with 3dB per octave, which may be difficult to see in a Matlab plot.

HTH,
Juergen

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