Started by in Matlab DSP9 years ago

I have 300sec data collected at 1Hz. I want to look at power spectrum of this time series, so first I need to do FFT(). But I am not sure if I...

I have 300sec data collected at 1Hz. I want to look at power spectrum of this time series, so first I need to do FFT(). But I am not sure if I need to pad it with zeros to make it 512. Matlab FFT() lets me do it either way, but I don't really understand which way I should do. Please advise. Thanks. > > using FFT() without padding zeros will not create any problems. the reason why we can go for

## FFT source code

Started by in Matlab DSP13 years ago 5 replies

Hi!! I'm new in this. I've just wanted to know if somebody have the source code of the fft library that uses matlab. Or if somebody knows how...

Hi!! I'm new in this. I've just wanted to know if somebody have the source code of the fft library that uses matlab. Or if somebody knows how does matlab do the fft algorithm. The things is that i have to export it to an embedded system and if i don't have the code i can't do the calculation of the fft Thanks Migel

## fft problem

Started by in Matlab DSP14 years ago 1 reply

Hi I've been having some problems with the fft() function in matlab. I ran a simple test... x = 0:1/460800:0.1; % sample rate =...

Hi I've been having some problems with the fft() function in matlab. I ran a simple test... x = 0:1/460800:0.1; % sample rate = 460800 Hz fx = sin(2*pi*30000*x); % sine wave @ 30000 Hz Y = fft(fx, 4096); % take first 4096 samples and fft Pyy = Y.*conj(Y); % power spectrum logPyy = 10*logPyy; % convert to dB f = 46080

## freqz vs FFT question

Started by in Matlab DSP7 years ago

Hi, I have always been confused about this two functions. Can someone please clarify why they behave this way? Let me give an example To me...

Hi, I have always been confused about this two functions. Can someone please clarify why they behave this way? Let me give an example To me it looks like that if we compute the impulse response of a filter, it should be the same thing as taking the FFT of that filter. But how come there is a difference? For example, let's say if I take the simple FFT of the following hamming window: L...

## FFT help needed

Started by in Matlab DSP13 years ago 1 reply

AOA I am stuck with a problem sir n need your immediate help. I get an EEG signal from net and try to process it. Q. What is the result of...

AOA I am stuck with a problem sir n need your immediate help. I get an EEG signal from net and try to process it. Q. What is the result of taking FFT of a signal? Q. What is on horizental and vertical axis when we plot result from FFT? I said that on x axis it is frequency in hertz but i was opposed and said that we have to do something more to the result of FFT to get frequency...

## doubt on amplitude of fft points

Started by in Matlab DSP11 years ago 1 reply

Hi everbody.I have a doubt.I am doing a problem of filtering(fir) in which we have to acquire our carrier precisely ..For that we have to do the...

Hi everbody.I have a doubt.I am doing a problem of filtering(fir) in which we have to acquire our carrier precisely ..For that we have to do the decimation, filtering(LPF) and down conversions(it is areal time application).TO check the frequency I have to do fft at each stage ..NOw the doubt comes is every time I do fft at each stage, the amlitude of fft peak decreases and it becomes very low at ...

Started by in Matlab DSP10 years ago 1 reply

I have 300sec data collected at 1Hz. I want to look at power spectrum of this time series, so first I need to do FFT(). But I am not sure if I...

I have 300sec data collected at 1Hz. I want to look at power spectrum of this time series, so first I need to do FFT(). But I am not sure if I need to pad it with zeros to make it 512. Matlab FFT() lets me do it either way, but I don't really understand which way I should do. Please advise. Thanks.

## Pruning FFT

Started by in Matlab DSP14 years ago

Dear all, I am looking for some Matlab code on pruning FFT or zoom FFT. Thank you, Esther

Dear all, I am looking for some Matlab code on pruning FFT or zoom FFT. Thank you, Esther

## fft problems

Started by in Matlab DSP14 years ago

Not sure I really understand your problem, but here's some code to help you out: N=1024; %length of zero padded fft x=0:100; ...

Not sure I really understand your problem, but here's some code to help you out: N=1024; %length of zero padded fft x=0:100; f=sin(2*x) + sin(3*x) + sin(4*x); F=fftshift(abs(fft(f,N))); w=-pi:2*pi/N:pi-(pi/N); %x scaled from -pi to pi plot(w,F) I hope that helps, feel free to e-mail me privately if you want an explanation.

## fft and matlab functions

Started by in Matlab DSP12 years ago

hi friends my question is why we should normalize fft to length of vector not to number of fft point (for plotting frequency response) the...

hi friends my question is why we should normalize fft to length of vector not to number of fft point (for plotting frequency response) the latter is what's the difference between crosscorr function and xcorr function in matlab appreciate thanks bye

## Re: FFT amplitude and frequencies

Started by in Matlab DSP13 years ago

Denilson- > Hello, i'm doing this code to see the FFT of 4 signals, all sin > waves, the only difference is they are at different...

Denilson- > Hello, i'm doing this code to see the FFT of 4 signals, all sin > waves, the only difference is they are at different frequencies. But > i'm having some problems in the amplitude of the FFT, it seems that > those that i'm having are not correct. > It is supposed to be 0.5 for all of them, i think. Before worrying about exact amplitude levels, it might help to clarify your obj

## fft amplitude and frequency

Started by in Matlab DSP14 years ago

Hi, I am new in this group. I am trying to apply fft on my data but it seems there is something that I don't understand. I searched...

Hi, I am new in this group. I am trying to apply fft on my data but it seems there is something that I don't understand. I searched previus posts but nothing helped me. Can anyboby help me to apply fft on this function, f(x) = sin(2*x) + sin(3*x) + sin(4*x) , x in [0 , b] b = 100 , 200 , 300 I have serious problems with the fre

## fft function in matlab and fft block in simulink dont match

Started by in Matlab DSP14 years ago

Hi, thanks to everyone who helped me with my last question, lots of responses and fast too :) I have a simulink model running...

Hi, thanks to everyone who helped me with my last question, lots of responses and fast too :) I have a simulink model running where I am performing FM and measuring adjacent channel power. I can't really quantitise this inside simulink so I send the output of my FM modulator to my workspace where I perform the FFT. During the

Started by in Matlab DSP14 years ago

hey guyz.... can anyone provide me with the internal structure of the fft block in the xilinx blockset....i have to design a new xilinx...

hey guyz.... can anyone provide me with the internal structure of the fft block in the xilinx blockset....i have to design a new xilinx library and it would be helpful to know wat already exists in these blocks....if neone has ever made a fft block for fixed point calculations...plz lemme know thanks, mayank

## About Frequency and FFT ?

Started by in Matlab DSP19 years ago

Hi! I can get the correct frequency value from below code: Fs = 100; n = 1/Fs:1/Fs:2; x = 0.8*sin(2*pi*10*n); z =...

Hi! I can get the correct frequency value from below code: Fs = 100; n = 1/Fs:1/Fs:2; x = 0.8*sin(2*pi*10*n); z = fft(x); N = length(z); z = abs(z(1:N/2+1)); freq = [0:N/2]/N*Fs; stem(freq,z);grid;zoom on; but, when I use fft(x

## Calculating SNR using FFT

Started by in Matlab DSP14 years ago

Hello, I am trying to calculate the SNR of signal that has just a DC component. Basically what I do is FFT with Kaiser window and I am...

Hello, I am trying to calculate the SNR of signal that has just a DC component. Basically what I do is FFT with Kaiser window and I am not sure what actually the FFT returns for the noise spectrum. Are those numbers the noise in a certain bandwidth (1.5 Hz as seen below) or this is the spectrum power density (1Hz)? The actual question is

## freq. components of a matrix

Started by in Matlab DSP16 years ago 1 reply

Hi, I want to find fractions of vertical and horizontal frequencies of "a" by the following commands: a= 1 4 7 10 2 5 8...

Hi, I want to find fractions of vertical and horizontal frequencies of "a" by the following commands: a= 1 4 7 10 2 5 8 11 3 6 9 12 13 14 15 16 p=fft(a); % fft of the matrix "a" in row-direction aT=a.'; q=fft(aT);

## Generating FFT coefficients

Started by in Matlab DSP17 years ago

hello, i need to generate a generic program in matlab that gives me the numeric values of the real and imaginary parts of the...

hello, i need to generate a generic program in matlab that gives me the numeric values of the real and imaginary parts of the twiddle factors used in FFT. I am designing an FFT processor and i need to store the values of these coefficients in a ROM. I am not very familiar with

## FFT vs freqz

Started by in Matlab DSP15 years ago 1 reply

hi, i have a low pass filter and i plotted the frequency response using freqz and fft and got diff plots... ...

hi, i have a low pass filter and i plotted the frequency response using freqz and fft and got diff plots... b=remez(102,[0 0.5 0.6 1],[1 1 0 0]); B = fft(b,1024); P = B.*conj(B); t=(pi/512)*[0:511]; figure(1); semilogy(t,P(1:512),'Color',[1 0 0.

## FFT Phase

Started by in Matlab DSP16 years ago

Hi, is there any function to change the phase of the algorithm of the fft in matlab? How could I do this? I am working with binary...

Hi, is there any function to change the phase of the algorithm of the fft in matlab? How could I do this? I am working with binary images and I need to calculate fft with a small change in the exponent of the exponential in the algorithm. Thanks Thank you all very much in adva