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Waveform Generation: Time Vectors and Sinusoids

Most toolbox functions require you to begin with a vector representing a time base. Consider generating data with a 1000 Hz sample frequency, for example. An appropriate time vector is

t = (0:0.001:1)';

where the MATLAB® colon operator creates a 1001-element row vector that represents time running from 0 to 1 s in steps of 1 ms. The transpose operator (') changes the row vector into a column; the semicolon (;) tells MATLAB to compute, but not display the result.

Given t, you can create a sample signal y consisting of two sinusoids, one at 50 Hz and one at 120 Hz with twice the amplitude.

y = sin(2*pi*50*t) + 2*sin(2*pi*120*t);

The new variable y, formed from vector t, is also 1001 elements long. You can add normally distributed white noise to the signal and plot the first 50 points using

rng default;
yn = y + 0.5*randn(size(t));
plot(t(1:50),yn(1:50))
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