Frequence of the signal

Hi , How I can calculate frequence of the signal in the matlab ?? Is there any function do that in matlab ?? can you give me sample example to do that .. Help me plazzzzze :"(

[Dr. Seis]

Are you trying to find the frequency spectrum of your signal? Or is your signal only one frequency and you are trying to find what that one frequency is? Or are you trying to figure out the instantaneous frequency at some location in your signal?

[Sean de Wolski]

Or how often your signal occurs?

[fatimah]

I am trying to find the frequency spectrum of signal.

Thank you for help

[Jan]

Who is plazzzzzze ?

Answer 1

[Paulo Silva]

From the MATLAB documentation of the fft function:

Fs = 1000;                    % Sampling frequency
T = 1/Fs;                     % Sample time
L = 1000;                     % Length of signal
t = (0:L-1)*T;                % Time vector
% Sum of a 50 Hz sinusoid and a 120 Hz sinusoid
x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); 
y = x + 2*randn(size(t));     % Sinusoids plus noise
plot(Fs*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')

NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);

% Plot single-sided amplitude spectrum.
plot(f,2*abs(Y(1:NFFT/2+1))) 
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')

%I added the next lines to find the value
%find maximum value, it should be the fundamental frequency (approximated)
[C,I]=max(2*abs(Y(1:NFFT/2+1)))
f(I)

[fatimah]

Thank you for helping :)

Can you tell me what is the different between heart beating frequency of the ECG and the frequency of the signals ??

Are you think it is the same ??

I am waiting for your response :)

Thanksssss

[Dr. Seis]

There will be some differences. I have seen enough TV that the signal of a beating heart on an EKG is not a perfect sinusoidal wave. It is also a little more complicated in that the pulse from a single heart beat is composed of more than one valve opening and closing. So, the lower frequency component should be associated with the frequency of each heart beat and the higher frequency component should be associated with orchestra of opening/closing valves during each heart beat.

[fatimah]

thank you for explaining.

can you give me code to calculate heart beating frequency of the ECG in matlab .

I need that :| to complete my work .

If you can't give me a code can you give me any advice to do that . :)

thank you again.

[Dr. Seis]

The above code is a good example. You will have to change things like the sampling frequency (i.e., Fs) and the vector you store your data in (i.e., x). Have you tried to copy/paste the above code into an .m file to see what it does or how it works? If you have questions about what each line does, try running it a few times with different values to see how it changes things (this is how most people learn new programming languages).

[Paulo Silva]

1- Find the peaks (findpeaks function from S.P. toolbox or similar code)

2- Find the time T between two of those peaks

3- F=1/T

[fatimah]

Elige Grant

&&

Paulo Silva

Thank you for cooperation :)

I am trying to do my best to finish my job