random signal delay

Question

zozo 2012-2-27

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回答： vijay 2013-10-31

clc
clear all
close all
fs=10000; % sampling frequency in Hz
f1=500; % frequency of signal in Hz
f2=200;
f3=700;
t_duration=1;    %duration of LONG signal in seconds
t = 0:1/fs:t_duration-1/fs; %sampling points
x = sin(2*pi*f1*t)+cos(2*pi*f2*t)+sin(2*pi*f3*t);
d=0.000079734452; % time delay in seconds

I can delay it mathematically as follows:

s1=sin(2*pi*f1*(t-d))+cos(2*pi*f2*(t-d))+sin(2*pi*f3*(t-d));

How can I do the same (mathematically) if:

x=randn(size(t));

I need to produce the same set of random values each time. I have gone through doc rng; but Iam unable to do it.

Please illustrate with an example.

thank you.

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Answer 1

Honglei Chen 2012-2-27

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There are two questions in your post so I'm not sure if I understand exactly what you look for. I'll include my thoughts below:

1. To get the same random value each time, set a seed using rng, for example

rng(1);
randn(10,1);
rng(1);
randn(10,1);

You should get the same random values for two trials.

2. Now if you want to delay the random signal, you can always append zero in front. The number of zeros you insert depends on your sampling frequency and required delay.

x = randn(10,1);
x_delay = [0;x];  % delayed by 1 sample

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zozo 2012-2-27

Ok..Can you suggest an alternative test, apart from the one I used above in my code?

Honglei Chen 2012-2-27

Personally I think your test case is fine, if you really want, you can try a triangle signal or even a rectangular signal. Just be prepared that there will be distortion in the result.

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