Kennedy asked . 2021-04-02

How to plot frequency spectrum of a signal in matlab?

close all;
%Define number of samples to take
fs = 8000;
f = 400; %Hz

%Define signal
t = 0:1/fs:1-1/fs;
signal = sin(2*pi*f*t);

%Plot to illustrate that it is a sine wave
plot(t, signal);
title('Time-Domain signal');

%Take fourier transform
fftSignal = fft(signal);

%apply fftshift to put it in the form we are used to (see documentation)
fftSignal = fftshift(fftSignal);

%Next, calculate the frequency axis, which is defined by the sampling rate
f = fs/2*linspace(-1,1,fs);

%Since the signal is complex, we need to plot the magnitude to get it to
%look right, so we use abs (absolute value)
figure;
plot(f, abs(fftSignal));
title('magnitude FFT of sine');
xlabel('Frequency (Hz)');
ylabel('magnitude');

%noise
noise = 2*randn(size(signal));
figure, plot(t,noise), title('Time-Domain Noise');
fftNoise = fft(noise);
fftNoise = fftshift(fftNoise);
figure, plot(f,abs(fftNoise)), title('Magnitude FFT of noise');
xlabel('Frequency (Hz)');
ylabel('magnitude');

%noisy signal
noisySignal = signal + noise;
figure, plot(t,noisySignal), title('Time-Domain Noisy Signal');
fftNoisySignal = fft(noisySignal);
fftNoisySignal = fftshift(fftNoisySignal);
figure, plot(f,abs(fftNoisySignal)), title('Magnitude FFT of noisy signal');
xlabel('Frequency (Hz)');
ylabel('magnitude');

matlab , signal , signal processing