Removing drift from EMG signal

i want to remove the drift from my emg signal that i obtained. i am using the following script

the original emg looks like this:

with the scipt above i get the following detrend:

u can see that the drift isnt completely removed, can anyone see what i am doing wrong or what i can change in my script to get the perfect result around y=0

thanks in advance!

[Star Strider]

One option woould be to calculate the fft of the signal to see where the low-frequency variations are, then using a highpass filter to pass everything above those frequencies. That should eliminate the baseline variations.

It will be necessary to experiment to determine the best cutoff frequency.

[Ben Halkon]

The problem with filtering is that it messes up the phase (which might need to be preserved for subsequent processing, e.g. subtraction of this signal from another; "zero phase shift" double-pass are never truly zero phase shift) and is never good at the beginning/end of the data (which generally has to be truncated).

[Star Strider]

There are other ways to remove a baseline shift. One I’ve used successfully uses the islocalmin function with 'MinProminence' and then fit a polynomial to those points. (This usually requires some experimentation.) After that, evaluate the polynomial on the entire independent variable vector, and subtract that result from the signal. The problem with using detrend for this is that it considers the entire signal. This method considers only the selected minima.

Answer 1

[Chunru]

%% detrend
% Remove polynomial trend

t = 0:20;
x = 3*sin(t) + t;
y = detrend(x);
plot(t,x,t,y,t,x-y,':k')
legend('Input Data','Detrended Data','Trend','Location','northwest')