Hi I need to write a code to plot the magnitude spectra of the following signals using MATLAB fft() function and relate the spectral lines with the constituent frequencies.

%this is the orginal functions that i need fft()

clc ; close all ;

t = 0: .02 : 4 * pi ;

x = zeros ( size ( t ) ) ;

for k = 1 : 2 : 19

x = x + sin ( k * t ) / k ; % Square wave

end

subplot (3,1,1)

plot (t, x )

title ( ' Square wave ' )

y = zeros ( size ( t ) ) ;

for k = 1 : 19

y = y- ( -1 ) ^ k * sin ( k * t ) / k ; % Sawtooth wave

end

subplot ( 3,1,2 )

plot ( t , y )

title ( ' Sawtooth wave ' )

z = zeros ( size ( t ) ) ;

for k = 1 : 2 : 19

z = z + cos ( k * t ) / ( k * k ) ; % Triangular wave

end

subplot ( 3,1,3 )

plot ( t , z )

title ( ' Triangular wave ' )

Answer 1

[Pravarthana P]

Hi Yafiet Solomon,

I understand that you are trying to plot the Magnitude spectra of the signals against their corresponding frequencies.

The "fft" function computes the discrete Fourier transform (DFT) of the input signal using a fast Fourier transform (FFT) algorithm. After computing the Fourier transform of the signal, compute the vector that depicts the signal’s sampling in frequency space. Finally, plot the computed signal’s FFT with their corresponding sampling frequency.

For more information refer to the documentation links below:

Fourier Transforms - MATLAB & Simulink (mathworks.com)

Fast Fourier transform - MATLAB fft (mathworks.com)

Hope this information helps you.