Amplitude of a signal

I have the attached signal. How can I get the voltage amplitude of this graph ?

This is a zoomed in graph:

Answer 1

[Mathieu NOE]

hello

• basically you want to plot the envelope of your data , there is a function for that :

envelope Envelope detector.

[YUPPER,YLOWER] = envelope(X) returns the upper and lower envelopes of

the input sequence, X, using the magnitude of its analytic signal.

it requires the Signal Processing Toolbox

• you may want to remove first the spikes , so a bit of low pass filtering / smoothing is needed

you can do that with smoothdata

If you don't have the Signal Processing Toolbox, see the demo below :

t = 0:0.01:10;
x = exp(-(t-5).^2/2).*sin(2*pi*5*t);

% obtain the envelope data
%--------------------------------------------
y = abs(hilbert(x)); % option 1 with hilbert
[up,down] = envelope2(t,x,'linear'); % option 2 with envelope2 (see below)

plot(t,x,t,y,'k',t,up,'m',t,down,'c')
legend('signal','hilbert','envelope2 / upper env','envelope2 / lower env');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [up,down] = envelope2(x,y,interpMethod)

%ENVELOPE gets the data of upper and down envelope of the known input (x,y).
%
%   Input parameters:
%    x               the abscissa of the given data
%    y               the ordinate of the given data
%    interpMethod    the interpolation method
%
%   Output parameters:
%    up      the upper envelope, which has the same length as x.
%    down    the down envelope, which has the same length as x.
%
%   See also DIFF INTERP1

%   Designed by: Lei Wang, <[e-mail]>, 11-Mar-2003.
%   Last Revision: 21-Mar-2003.
%   Dept. Mechanical & Aerospace Engineering, NC State University.
% $Revision: 1.1 $  $Date: 3/21/2003 10:33 AM $

if length(x) ~= length(y)
    error('Two input data should have the same length.');
end

if (nargin < 2)|(nargin > 3),
 error('Please see help for INPUT DATA.');
elseif (nargin == 2)
    interpMethod = 'linear';
end

% Find the extreme maxim values 
% and the corresponding indexes
%----------------------------------------------------
extrMaxIndex = find(diff(sign(diff(y)))==-2)+1;
extrMaxValue = y(extrMaxIndex);

% Find the extreme minim values 
% and the corresponding indexes
%----------------------------------------------------
extrMinIndex = find(diff(sign(diff(y)))==+2)+1;
extrMinValue = y(extrMinIndex);

up = extrMaxValue;
up_x = x(extrMaxIndex);

down = extrMinValue;
down_x = x(extrMinIndex);

% Interpolation of the upper/down envelope data
%----------------------------------------------------
up = interp1(up_x,up,x,interpMethod); 
down = interp1(down_x,down,x,interpMethod); 
end

[Mathieu NOE]

Hello

Problem solved ?

would you mind accepting my answer ? thanks !