Linear envelope of an EMG signal

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Ines Shekhovtsov 2022-11-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1866773-linear-envelope-of-an-emg-signal

评论： Mathieu NOE 2022-12-7

Hello,

I am trying to plot an RMS envelope over a single EMG signal from a respiratory muscle. The data was collected at 2000Hz. Prior to envelope calculation and plot i bandpassed the signal using a 6th order butterworth filter from 30-300Hz. For my envelope calculation, i have the following code:

[up,lo]=envelope(RUT,100,'rms');

I wish to plot the upper envelope on top of the original signal and so my code is:

plot(Time,RUT,Time,up,'lineWidth',0.1)

I am expecting the upper envelope to be higer up to the top of the signal and am not sure why it isn't. In all of the examples i've seen for Matlab, the upper envelope hugs the sigal more close to the top. So i am just curious if i did something wrong and what i can do to correct it.

Thank you in advance! My reference figure screenshot is attached below

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Answer 1

Mathieu NOE 2022-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/1866773-linear-envelope-of-an-emg-signal#answer_1116213

在 MATLAB Online 中打开

hello Ines

there is no bug here , the plot is correct vs what matlab is supposed to do

when you select 'rms' option, you cannot have the envelope on the 'top' of signal , because the rms of a signal is always less than the spikes amplitude.

here the demo code (from the matlab help) :

load('train');
envelope(y,150,'rms');

will give you this result (lo and up envelopes are displayed here)

now if you use 'peak' option, this is maybe what you wanted :

envelope(y,150,'peak');

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Mathieu NOE 2022-12-6

在 MATLAB Online 中打开

hello again

try this

t = tiledlayout(2,2,'TileSpacing','Compact');
n=100;
x=linspace(0,2*pi,n);
buffer = 10;  %  buffer size in samples
% Tile 1
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
% Tile 2
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
% Tile 3
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
% Tile 4
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);

Mathieu NOE 2022-12-6

在 MATLAB Online 中打开

simply add this line where you don't want the X labels

set(gca, 'XTickLabel', [])

here the full code and resuts , the 2 upper plots are modified by not the bottom ones

t = tiledlayout(2,2,'TileSpacing','Compact');
n=100;
x=linspace(0,2*pi,n);
buffer = 10;  %  buffer size in samples
% Tile 1
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
set(gca, 'XTickLabel', [])
% Tile 2
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
set(gca, 'XTickLabel', [])
% Tile 3
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);
% Tile 4
nexttile
data = 50*abs(sin(x) + 0.25*randn(size(x)));
a_rms=sqrt(movmean(data.^2,buffer)); % moving RMS 
plot(x,data,x,a_rms,'r');
legend('raw','rms');
% put some text above rms curve
pos_x = mean(x); % centered on x axis
pos_y = 0.5*(max(a_rms) + max(data)); % half way between max of rms curve and max of raw data
text(pos_x,pos_y,num2str(round(max(a_rms))),'FontSize',25);

Ines Shekhovtsov 2022-12-6

Thank you for your help!

Mathieu NOE 2022-12-7

as always, my pleasure !

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Linear envelope of an EMG signal

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Linear envelope of an EMG signal

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