find slope sign change of emg signal

dear

i want to find slope sign change of emg signal.

how i do this?

Thank you

Answer 1

[KSSV]

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

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

[Ali Asghar]

dear

my data signal is 30000x4

time is 1x30000

its show error : Matrix dimensions must agree.

Answer 2

[Star Strider]

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.