play white noise for certain time

Hi I have few questions. I want to play a white noise sound for 20 ms, but I am not sure how to check which frequencies are used to produce white noise. This is the code I am using: x=wgn(200,1,0); sound(x,10000)

But I don't think this is producing what I want. Also I have a doubt: the matrix x contains values from -3 to +3, but I don't see why. I would expect those to be the frequencies, but if I generate a white noise then the frequencies should range from 20 Hz to 20 kHz, right?

[KSSV]

A white noise has all possible frequencies. To achieve what you want....you need to generate white noise and filter out the unwanted frequencies.

[Salvatore Lacava]

when you say all possible frequencies do you mean limited to the specifactions of your speakers/computer? Or does white noise includes ultrasound and so on?

[Wooshik Kim]

This might help

https://www.mathworks.com/matlabcentral/answers/71959-how-to-generate-white-noise-of-particular-frequency-in-matlab

[Wooshik Kim]

Also you can use fft to analyze the frequency spectrum of your noise

[Salvatore Lacava]

Hi, so if I apply fft on the matrix I get a bunch of negative values from -100 to +100. Those can't be frequency, so do you have an idea of what I am looking at, and how to visualize the frequencise used?

[Aquatris]

Follow the example from Matlabs website for fft , where they explain how to take fft of a signal.

[Salvatore Lacava]

Your link is broken

Answer 1

[Hengameh Noshahri]

Fs = 96000; % sampling frequency in Hz

Ts = 1/Fs; % sampling time in seconds

te = 5; % signal duration in seconds

y = randn(te*Fs,1); % generate White noise of duration te

t = 0:Ts:te; % generate a time array

N = size(t,2); % size of the signal

N = pow2(nextpow2(N)); % change N for efficiency in FFt calculation

Freq = Fs/2 * linspace(0, 1, N/2+1); % generate a frequency array

Y = fft(y,N)*(N-1)*Ts/N; % calculate FFT of the signal

YMag = abs(Y); % magnitude of FFT signal

plot(Freq,YMag(1:N/2+1)), ylabel('FFT'), xlabel('Frequency [Hz]')

sound(y,Fs,24); % listen to the generated noise if you feel adventurous!