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sine wave plot

Asked by aaa
on 24 Apr 2012
Latest activity Commented on by Nauman Hafeez on 28 Dec 2018
Hi,
I am having some trouble plotting a sine wave and i'm not sure where i am going wrong.
i have
t = [0:0.1:2*pi]
a = sin(t);
plot(t,a)
this works by itself, but i want to be able to change the frequency. When i run the same code but make the change
a = sin(2*pi*60*t)
the code returns something bad. What am i doing wrong? How can i generate a sin wave with different frequencies?

  2 Comments

How many cycles do you need in drawing?
in sine function in MATLAB it is always sin(wt). here frequency w is in radian/sec not f (in HZ) so w will give you the no.of the cycle.
suppose w=1 it is one cycle and so on
if you want to use the sin(2*pi*60*t) you can use the sind(2*pi*9.545*t). why i use the 9.545 bcz we should convert the f to w in the time interval of 2*pi.

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4 Answers

Answer by Rick Rosson
on 24 Apr 2012
 Accepted Answer

Please try:
%%Time specifications:
Fs = 8000; % samples per second
dt = 1/Fs; % seconds per sample
StopTime = 0.25; % seconds
t = (0:dt:StopTime-dt)'; % seconds
%%Sine wave:
Fc = 60; % hertz
x = cos(2*pi*Fc*t);
% Plot the signal versus time:
figure;
plot(t,x);
xlabel('time (in seconds)');
title('Signal versus Time');
zoom xon;
HTH.
Rick

  2 Comments

Thanks for your reply & detailed answer.
How to calculate Fs for a particular frequency signal?
I am generating a stimulating signal using matlab for my impedance meter and it gives me different results on different Fs.

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Answer by Mike Mki
on 29 Nov 2016

Dear Mr. Rick, Is it possible to create knit structure in Matlab as follows:

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Answer by omphile hahilton on 3 Mar 2015

I would like to generate the product of 2 sine waves at frequencies 697Hz and 1209Hz and sample them and then generate the spectrum of the signal. then play the sine wave through my soundcard speakers help me..........thanks in advanced

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Answer by Robert
on 28 Nov 2017

aaa,
What goes wrong: by multiplying time vector t by 2*pi*60 your discrete step size becomes 0.1*2*pi*60=37.6991. But you need at least two samples per cycle (2*pi) to depict your sine wave. Otherwise you'll get an alias frequency, and in you special case the alias frequency is infinity as you produce a whole multiple of 2*pi as step size, thus your plot never gets its arse off (roundabout) zero.
Using Rick's code you'll be granted enough samples per period.
Best regs
Robert

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