find slope sign change of emg signal

Asked by Ali Asghar on 16 Aug 2019

Latest activity Answered by Star Strider on 18 Aug 2019

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dear

i want to find slope sign change of emg signal.

how i do this?

Thank you

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Answer by KSSV on 16 Aug 2019

If (t,x) is your time and signal.

dt = diff(t) ; 
dx = diff(x) ; 
slope = dx./dt ; 
slope_sign = sign(slop) ; 

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Ali Asghar on 18 Aug 2019

dear

my data signal is 30000x4

time is 1x30000

its show error : Matrix dimensions must agree.

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Answer by Star Strider on 18 Aug 2019

Use the gradient function to produce results that are the same sizes as your data, not diff.

If ‘EMG’ is your (30000x4) signal matrix, the derivative (‘dEMG’) is:

[~,dEMG] = gradient(EMG);

Note that taking the derivative of a a ‘real world’ signal will significantly amplify the noise. It would be best for you to use a lowpass filter on your EMG signal matrix first, to eliminate high-frequency noise. If you have R2018a or later, use the lowpass function (or bandpass if you also want to eliminate d-c offset and low-frequency baseline drift). Otherwise, efficient filters are not difficult to design and implement in MATLAB.

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