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How to separate signals with diffrent frequencies

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t = linspace(0, 1, 1001);
x=sin(2*pi*t*3) + sin(2*pi*t*6) + sin(2*pi*t*10)+sin(2*pi*t*13)+sin(2*pi*t*20)+sin(2*pi*t*50)+sin(2*pi*t*100)+sin(2*pi*t*200);
% my signal with frequencies 3,6,10,13,20,50,100,200 KHz
y=x+randn(size(x)).*sigma; % adding noise
I filtered the signal using fft.
I want to separate signals.
Eg : from my original signal, I want a signal with frequency range say 3 to 8 KHz, another signal say from 100 to 200 KHz. How can I separate them and display those signals.How can I do this. Anybody Please help me to solve this.?


mouh nyquist
mouh nyquist on 1 Jan 2015
you must read about chebishev and butter filter
aarthi arunachalam
aarthi arunachalam on 11 Mar 2016
i too want to seperate certain frequency range from my original signal. can you help me?

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Accepted Answer

Shoaibur Rahman
Shoaibur Rahman on 1 Jan 2015
Add the following lines of code at the bottom of your code (after y=x+randn(size(x)).*sigma;):
ffty = fft(y);
ffty = abs(ffty(1:ceil(length(y)/2)));
[~,locs] = findpeaks(ffty);
freqs = (locs-1)/t(end)
signal_1 = sin(2*pi*t*freqs(1))+sin(2*pi*t*freqs(2))+sin(2*pi*t*freqs(3)); % 3-10
signal_2 = sin(2*pi*t*freqs(6))+sin(2*pi*t*freqs(7)); % 50-100
subplot(211), plot(t,signal_1)
subplot(212), plot(t,signal_2)


Show 7 older comments
Srey on 1 Jan 2015
How can we then plot those signals, if frequencies are present in the signal.
Shoaibur Rahman
Shoaibur Rahman on 1 Jan 2015
Use any sinusoidal function to generate a signal with that frequency, and then plot that against time. For example:
t = .....
out1 = sin(2*pi*f1*t);
out2 = cos(2*pi*f2*t);
This is just from the Fourier analysis, that states any signal (with some criteria) can be represented as summation of infinite sinusoidal functions. So, to represent only one frequency, use one sinusoidal function, or to represent multiple frequency components, use summation of multiple sinusoidal functions with those frequencies.

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More Answers (1)

Pourya Alinezhad
Pourya Alinezhad on 1 Jan 2015
1-you can use several filters with different center frequencies (chebishev or butter filter)
h = fdesign.bandpass('N,F3dB1,F3dB2', N, Fc1, Fc2, Fs);
Hd = design(h, 'butter');
filter (Hd,input_signal);
2- you can use an adaptive filter and feed the signal and the desired signals to it (LMS filter).


Srey on 1 Jan 2015
I want a signal with freq range:say 3-10Hz and another signal with freq say 50-100. I want to plot them separately.How can be done from my original signal
Pourya Alinezhad
Pourya Alinezhad on 1 Jan 2015
assign Fc1, Fc2 values as 3 and 10Kz for a filter. then make another filter with 50 to 100 kHz spectrum.

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