Clear Filters
Clear Filters

How to plot the spectrum of the sum of sine waves

23 views (last 30 days)
pq
pq on 7 Apr 2016
Moved: Voss on 27 Feb 2024
I need to plot the spectrum of the sum of 3 sine waves (100 Hz & 20 dB SPL, 300 Hz& 30 dB SPL, and 400 Hz & 15 dB SPL). This is what I have so far, but the amplitude on the y axis seems wrong.
% Sampling
fs = 1000; % Sampling rate [Hz]
Ts = 1/fs; % Sampling period [s]
fNy = fs / 2; % Nyquist frequency [Hz]
duration = 10; % Duration [s]
t = 0 : Ts : duration-Ts; % Time vector
noSamples = length(t); % Number of samples
A_1 = 20;
A_2 = 30;
A_3 = 15;
f_1 = 100;
f_2 = 300;
f_3 = 400;
s_1 = A_1*sin((2*pi*f_1*t));
s_2 = A_2*sin((2*pi*f_2*t));
s_3 = A_3*sin((2*pi*f_3*t));
% Contaminated signal
xn = s_1+s_2+s_3;
% Frequency analysis
f = 0 : fs/noSamples : fs - fs/noSamples; % Frequency vector
% FFT
x_fft = abs(fft(x));
xn_fft = abs(fft(xn));
% Plot
plot(f,xn_fft);
xlim([0 fNy]);
xlabel('Frequency (Hz)')
ylabel('Amplitude (dB SPL)')
title('{Spectrum}')
  2 Comments
Joyce
Joyce on 27 Feb 2024
Moved: Voss on 27 Feb 2024
Generate a composite signal by summing 2 sine waves of frequencies 100HZ and 300 HZ APPLY FFT components write matlab program to plot magnitude spectrum

Sign in to comment.

Answers (1)

Rick Rosson
Rick Rosson on 10 Apr 2016
x_fft = abs(fft(x)/noSamples);
xn_fft = abs(fft(xn)/noSamples);

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!