how to make an envelope of a signal?

He,

I have some trouble with making an envelope of a noisy signal with Matlab. Is there some function to do this?

Answer 1

[Image Analyst]

Try morphological dilation and erosion - they're the local max and min. Use imdilate and imerode if you have the image processing toolbox.

numberOfSamples = 200;
t = linspace(0, 4*pi, numberOfSamples);
decay = exp(-t);
y = 10 .* sin(t) .* exp(-t) + rand(1, numberOfSamples);
plot(t, y, 'r-');
grid on;
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

upperEnvelope = imdilate(y, true(1, 9));
lowerEnvelope = imerode(y, true(1, 9));
hold on;
plot(t, upperEnvelope, 'b-', 'LineWidth', 2);
plot(t, lowerEnvelope, 'b-', 'LineWidth', 2);

Or try this File Exchange submission: http://www.mathworks.com/matlabcentral/fileexchange/27662-evolve-top-and-bottom-envelopes-for-time-signals-i-e

Answer 2

[Andrei Bobrov]

Use rand, randn, etc.

eg

x = linspace(0,2*pi,300);
sx = sin(x);
out = sx + .2*(2*rand(size(x)) - 1);

plot(x,sx,'b.',x,out,'r*'); grid on

[sunil kalyankar]

i have data in time domain envelope analysis pls help me in writing matlab code pls pls

[Image Analyst]

There are now boundary() and envelope() functions in MATLAB. Try them.

Answer 3

[Daniel Shub]

You could use the Hilbert Transform.