low-pass filtering a signal within a range determined by signal amplitude

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Jose Rego Terol 2020-12-15

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https://ww2.mathworks.cn/matlabcentral/answers/694290-low-pass-filtering-a-signal-within-a-range-determined-by-signal-amplitude

评论： Mathieu NOE 2020-12-15

采纳的回答： Mathieu NOE

filtering.jpg

Hi all,

I have this problem (see the picture attached). The baseline is noisy, so I have applied a lowpass filter (1 Hz, y=lowpass(I_P,1,6250). The data looks amazing but the spikes are smaller (of course, because I applied a low-pass filter).

So, in short, I want to apply the same low-pass filter (1Hz) exclusively to the baseline, i.e. from -10 pA to + 50 pA, so that the data baseline is improved signal-wise, and the spike amplitude remains untouchable (keeping the real amplitude).

The signal inside the green box is the data I want to filter. The signal inside the red box is the data I do not want to filter.

Thanks

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采纳的回答

Mathieu NOE 2020-12-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/694290-low-pass-filtering-a-signal-within-a-range-determined-by-signal-amplitude#answer_575955

在 MATLAB Online 中打开

myslidingavg.m

hello Jose

so this is a little code snipset, it uses a windowing technique as low pass filter

the peaks are left as original

you can leave the peks very sharp (one point) or wider if you leave the following line active :

hope it helps !!

%% signal generation
signal = 10*randn(1,samples); % noise
% add some peaks (must NOT be filtered)
signal(100) = 400;
signal(200) = 300;
signal(300) = 200;
signal = myslidingavg(signal, 5); % just a trick to make the peaks a bit wider (optionnal)
%% main code
% sliding avg method
threshold = max(abs(signal))/4;
ind = find(signal< threshold);
out = myslidingavg(signal(ind), 100);
signal_out = signal;
signal_out(ind) = out;
figure(2),
plot(time,signal,'b',time,signal_out,'r');

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Jose Rego Terol 2020-12-15

Dear Mathieu,

At the beginning, I was sceptic about the utility of your code for my needs.

I have been playing around with your code. Now, I understand that this is what I need.

Please, let me encourage you to submit this code to File Exchange. It would be beneficial for everyone in our situation, and you just submitted here in this thread. Then, why don´t you make it more visible, more accessible?

In short, good job and thanks for sharing this code with me.

Best,

Jose