# generate signals with different SNR

76 views (last 30 days)
nauman on 13 Jan 2018
Commented: Shae Morgan on 30 Oct 2020 at 11:43
Hello all
I need to generate random white Gaussian noise of 3 second length. I also need to add 03 sinusoidal (say 10 KHz) pulses of 100 ms duration and SNRs of 1 dB, -10 dB and -20 dB respectively at random locations in 3 sec length Gaussian noise.
Can any one kindly help me with MATLAB code?
Also how can i verify the results i.e. the required SNR has been generated?
Thanks

Image Analyst on 13 Jan 2018
What's your sampling rate? How many elements do you want to use to represent this 3 second length?
nauman on 14 Jan 2018
My sampling rate is 100 K samples/s. This will result in 300 K samples for 3s length signal
nauman on 3 Feb 2018
Any help in this regard is highly appreciated plz.

Shae Morgan on 7 Aug 2020
Edited: Shae Morgan on 30 Oct 2020 at 11:43
Here's a solution! Hope it's helpful
%setup
fs=100000;
noise_dur=3;
sine_freq=10000;
sine_dur=.1;
t=0:1/fs:sine_dur-1/fs;
snr=[1,-10,-20];
sine_samps=sine_dur*fs;
%generate noise
noise=randn(fs*noise_dur,1); %generate gaussian noise
norm_noise=noise./max(noise); %scale noise
rms_noise=rms(norm_noise); %get the rms amplitude to which the sines will be compared
%generate the 3 signals at the 3 SNRs and check
for i=1:length(snr)
amp=10^(snr(i)/20)*rms_noise;
x=sin(2*pi*sine_freq*t);
xt(i,:) = (x./rms(x)).*amp;
check_snr=20*log10(rms(xt(i,:))/rms_noise)
end
%set random location 1
a=1;
b=length(noise)-sine_samps;
idx1=round(rand()*(b-a)+a);
%get random location 2 that doesn't overlap with 1
overlap=1;
while overlap==1
idx2=rand()*(b-a)+a;
if idx2<=idx1-sine_samps || idx2>idx1+sine_samps
overlap=0;
end
end
idx2=round(idx2);
%get random location 3 that doesn't overlay 1 or 2
overlap=1;
while overlap==1
idx3=rand()*(b-a)+a;
if idx3<=idx1-sine_samps || idx3>idx1+sine_samps
if idx3<=idx2-sine_samps || idx3>idx2+sine_samps
idx3=round(idx3);
overlap=0;
end
end
end
%set the locations of the stimuli and pad zeros in between
[loc,idx]=sort([idx1 idx2,idx3]);
%combine,play,and plot final sound
final=stim+norm_noise;
sound(final,fs)
plot(final) %stimulus is masked by the noise
plot(stim) %plot to see the stimuli

Shae Morgan on 7 Aug 2020
If you want to make sure that the local SNR is exact, you'll need to find the RMS of the samples of noise at the times where the tones are played, and then set the amplitude of the sine waves based on a comparison there.
Daniel May on 29 Oct 2020 at 16:50
I believe:
final=stim+noise;
should be:
final=stim+norm_noise;
-Daniel
Shae Morgan on 30 Oct 2020 at 11:43
@Daniel - thanks for catching! I updated to reflect this

nauman on 19 Jan 2018
Hi all
Any help plz?
Thanks