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adding 5% white gaussian noise

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Hi everyone;
I need to add 5% noise to my signal (amplitude of noise = 0.05* signal amplitude) using "randn" as:
signal_noisy=signal+0.5*randn(signal) % (is it correct?)
is the genereated noise, whight gussion one?!
if I want to use "awgn" is it correct to say in this case SNR=13 ???
I realy appriciate your help here

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Accepted Answer

Image Analyst
Image Analyst on 4 Jul 2020
Try this:
% Make sample data.
x = linspace(0, 3*pi, 640);
period = 2*pi;
y = cos(2 * pi * x / period); % Noise-free signal.
% Noise is 5% of the signal value at each location,
% which means sigma is not a constant at each location.
amplitudes = y * 0.05;
noise = amplitudes .* randn(1, length(y));
% Add the noise to the noise-free signal.
yNoisy = y + noise;
% Plot everything.
plot(x, yNoisy, 'r.', 'MarkerSize', 8);
hold on;
plot(x, y, 'b-', 'LineWidth', 2);
grid on;

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atabak mostafavi
atabak mostafavi on 4 Jul 2020
great thank you; and would this method generate gussion ( flat spactrum ) noise since I am trying to model the measurement noise and it kinda important to be flat spactrum.
Image Analyst
Image Analyst on 4 Jul 2020
Yes, it's flat. The noise depends only on the signal and there is no spatial or time dependency on it, other than the signal itself of course.

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