How to plot frequency spectrum of a signal in matlab?

Neeta Dsouza answered . 2025-02-28 04:40:12

close all;
clear;

% Define parameters
fs = 8000;          % Sampling frequency in Hz
f = 400;            % Signal frequency in Hz
t = 0:1/fs:1-1/fs;  % Time vector (1 second duration)

% Define signal
signal = sin(2*pi*f*t);

% Plot time-domain signal
figure;
plot(t, signal);
title('Time-Domain Signal');
xlabel('Time (s)');
ylabel('Amplitude');

% Compute FFT
N = length(signal);             % Number of samples
fftSignal = fft(signal);        % Perform FFT
fftSignal = fftSignal / N;      % Normalize FFT output

% Compute frequency axis
f = (0:N-1)*(fs/N);             % Frequency vector (0 to fs)
halfRange = 1:floor(N/2);       % Consider only the positive frequencies

% Plot frequency spectrum
figure;
plot(f(halfRange), abs(fftSignal(halfRange))); % Magnitude spectrum
title('Frequency Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Magnitude');

% Add noise
noise = 2*randn(size(signal));  % Generate random noise
noisySignal = signal + noise;   % Add noise to the signal

% Plot time-domain noisy signal
figure;
plot(t, noisySignal);
title('Time-Domain Noisy Signal');
xlabel('Time (s)');
ylabel('Amplitude');

% Compute FFT of noisy signal
fftNoisySignal = fft(noisySignal);
fftNoisySignal = fftNoisySignal / N;

% Plot frequency spectrum of noisy signal
figure;
plot(f(halfRange), abs(fftNoisySignal(halfRange))); % Magnitude spectrum
title('Frequency Spectrum of Noisy Signal');
xlabel('Frequency (Hz)');
ylabel('Magnitude');

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