Arguments in Plot function

Question

The following Matlab scrip (taken from MATLAB help for fft) runs perfectly fine

Fs = 1000;                    % Sampling frequency
T = 1/Fs;                     % Sample time
L = 1000;                     % Length of signal
t = (0:L-1)*T;                % Time vector
% Sum of a 50 Hz sinusoid and a 120 Hz sinusoid
x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); 
y = x + 2*randn(size(t));     % Sinusoids plus noise
plot(Fs*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')

enter image description here

But I am unable to understand why we needed Fs*t in plot(). Why I am making it dimension less?

If this is strange, then what did you expect? (And what happens if you try to plot that) — Dennis Jaheruddin
– Dennis Jaheruddin, Commented Feb 8, 2013 at 10:15

Jan · Accepted Answer · 2013-02-08 10:22:14Z

2

Your vector t is defined in terms of samples, i.e. t(10) is the value taken as the 10th sample.

If you want to plot the signal vs. time, you will have to multiply the sampling instance with the sampling time, i.e. time = FS*t .

If you don't scale, you eventually plot the signal vs. the sampling instances. Then, however, the label "time(ms)" is not correct.

answered Feb 8, 2013 at 10:22

Jan

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