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--- visual3d:documentation:emg:filtering:integrate_emg [2024/06/17 17:03] – removed sgranger
+++ visual3d:documentation:emg:filtering:integrate_emg [2024/07/17 15:45] (current) – created sgranger
@@ Line 1: / Line 1: @@
+====== Integrate EMG ======
+===== Linear Envelope =====
+=== Computing the EMG Envelope using rectify and lowpass filter ===
+This section will compute the EMG Envelope using rectify and lowpass filter. Rectify takes the absolute value of every element of a signal. Visual3D calculates signal rectification using the following formula: x(ti)= abs(x(ti))
+=== Lowpass Filter Cutoff ===
+The default lowpass filter in Visual3D is a fourth order butterworth filter.
+Butterworth filters have an upper limit on the magnitude of the cutoff frequency.
+The maximum theoretical cutoff frequency is (sampling_rate*0.802/2).
+VIsual3D is a little more conservative than that because we have found the filter to be unreliable at the theoretical limits.
+The highest cutoff frequency that VIsual3D will allow you is 0.393* sampling-rate.
+If your EMG signals are sampled at 1000 Hz, the highest cutoff frequency is 393 Hz.
+=== Example Script ===
+The highpass filter is not part of the linear envelope, but is used to remove the [[Visual3D:Documentation:EMG:Processing:Detecting_Muscle_Onset|DC offset]].
+<code>
+! Apply high pass filter with 50 hz cutoff
+Highpass_Filter
+/Signal_Types=ANALOG
+/SIgnal_Names=EMG1+EMG2+EMG3
+/Signal_Folder=ORIGINAL
+! /Result_Suffix=
+/Result_Folder=HIGHPASS
+! /Filter_Class=BUTTERWORTH
+/Frequency_Cutoff=50
+/Num_Reflected= 0
+/Total_Buffer_Size=100
+/Num_Bidirectional_Passes=1
+;
+! Rectify the signals
+Rectify
+/SIGNAL_TYPES=ANALOG
+/SIGNAL_NAMES=EMG1+EMG2+EMG3
+/SIGNAL_FOLDER=HIGHPASS
+! /RESULT_NAMES=
+! /RESULT_TYPES=
+/RESULT_FOLDER=RECTIFY
+! /RESULT_SUFFIX=
+;
+! Apply a low pass filter
+Lowpass_Filter
+/Signal_Types= ANALOG
+/Signal_Names= EMG1+EMG2+EMG3
+/Signal_Folder= RECTIFY
+! /Result_Suffix=
+/Result_Folder=LOWPASS
+/Frequency_Cutoff=10
+/Num_Reflected=50
+;
+</code>