MATLAB: How to generate noise with particular frequency

digital signal processingMATLAB

Hi. I want to generate a noise with a certain frequency, for example 10kHz but I do not know how to. So I just proceed with this code:
% Open standard demo sound that ships with MATLAB.
[perfectSound, freq] = audioread('music.wav');  
noise = 0.1*randn(size(perfectSound));
% Play noise
soundsc(noise, freq);
% Get sampling frequency
t=0:1/freq:(length(noise)-1)/freq; 
figure(1);
plot(t,noise);
title('Noise');
ylabel('Amplitude');
xlabel('Length (in Second)');
% Graph it
n=length(noise)-1;
f=0:freq/n:freq;
wavefft=abs(fft(noise));%perform Fourier Transform
figure(2);
plot(f,wavefft);%plot Fourier Transform
xlabel('Frequency in Hz');
ylabel('Magnitude');
title('Noise FFT');
Then, result that I got is:
From workspace, the noise frequency is 44100 Hz. What should I do if I want to generate noise with different frequency?

Best Answer

Noise (‘white’ noise) is by definition broadband, so it does not have a specific frequency. You can create a 10 kHz signal with noise, but that is as close as you can get to doing what you want.
For example:
len = 15;                                       % Length (sec)
f   = 1E+4;                                     % Frequency (Hz)
Fs  = 8192;                                     % Sampling Frequency (Hz)
t   = linspace(0, len, Fs*len);                 % Time Vector
signal = sin(2*pi*f*t);                         % Signal (10 kHz sine)
sound(signal, Fs)                               % Original Signal
noise = signal + 0.1*randn(size(signal));
pause(15)                                       % Wait For First Sound To Finish Playing
sound(noise, Fs)                                % Noisy Signal
You could also create and use an audiplayer object with playblocking, instead of inserting a pause call.
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