How to Add random noise to a signal

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lady bird
lady bird 2015-5-20
编辑： DGM 2023-3-4
hello all
please can ou help me out adding a noise signal to my system.
i tried adding a sinus function , but i would like to add a random noise signal rather than the sinus function. I'm running simulation from 1 to 3000
if k>1000 & k<2000
dk(k)=sin(12*k*pi*ts);
x=A*x+B*u(k)+B*dk(k);
else
dk(k)=0;
x=A*x+B*u(k);
end
Thank you so much
Best regards
  2 个评论
chris matthew
chris matthew 2020-3-14
移动：DGM 2023-3-4
how to add noise to audio not for signal
Image Analyst
Image Analyst 2020-3-14
移动：DGM 2023-3-4
What does that mean? Audio IS a signal. You can't add noise to audio without adding it to the signal that defines the audio waveform.

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回答（6 个）

Thorsten
Thorsten 2015-5-20
x = linspace(-2*pi, 2*pi);
plot(sin(x) + 0.5*rand(size(x)))
  5 个评论
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Image Analyst
Image Analyst 2020-2-12
Tuhin, you can have the amplitude vary with the signal amplitude if you want. For example
% Create noise-only signal.
noisy_signal = rand(size(noise_free_signal));
% Create an amplitude for that noise that is 10% of the noise-free signal at every element.
amplitude = 0.1 * noise_free_signal;
% Now add the noise-only signal to your original noise-free signal to create a noisy signal.
% Be sure to use .*, not *, so that you do element-by-element multiplication.
noisy_signal = noise_free_signal + amplitude .* rand(size(noise_free_signal));
% Adjust amplitude to control the amount of noise.
Now the noise - the max possible noise amplitude - will vary according to the noise-free signal amplitude. Of course since it's noise, the noise won't always be the max possible, it will be less, but it could potentially get that high.
Tuhin Choudhury
Tuhin Choudhury 2020-3-16
编辑：Tuhin Choudhury 2020-3-16
Hi,
Thanks. This would be more of a flexible scaling of the noise w.r.t the input signal.
BR- Tuhin

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Image Analyst
Image Analyst 2015-5-20
So just use rand() instead of sin().
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Prajakta Yeola
Prajakta Yeola 2017-10-29
Can we use the same code if audio signal is .wav file? i.e. if x is a .wav file
Image Analyst
Image Analyst 2017-10-29
Sure, just figure out the amplitude and add it
yNoisy = yOriginal + amplitude * rand(1, length(yOriginal));

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KL
KL 2015-5-20
Did you check the gaussian noise function?
  2 个评论
lady bird
lady bird 2015-5-20
i found a awgn function but i dont know how to use it in my case?
KL
KL 2015-5-20
There's a difference between wgn() and awgn(). With the latter, you add noise throughout the whole range. I understand you want to add noise between certain time intervals. So in this case, I would suggest to use wgn(). At the moment I do not have the toolbox to use this function. Anyhow you shall use this function to calculate the noiseSignal variable according to @Image Analyst's code.

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Aparna Gupta
Aparna Gupta 2017-6-21
Can anyone please help me with the code to add awgn noise to an eeg signal,which i have taken from a database and the file is of .mat type?
Mohammad Sohail Khan
编辑：DGM 2023-3-4
t = 0:pi/100:40;
x = cos(pi/10*t)+0.5*randn(size(t));
plot(t,x)
Then you know where pi/2, 3pi/4 etc are.
Adewale Obaro
Adewale Obaro 2018-9-24
编辑：DGM 2023-3-4
N = 1000;
t = 0:1/N:2;
x = sin(2*pi*5*t);
Noise = x + randn(1,N)';
plot(t,Noise);
title('Noise in the Amplitude interval (0,0,1,0)');
ylabel('Amplitude [m]')
xlabel('Time [s]')

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