Hello, I am having some questions related to FFT while using inbuilt Matlab or Octave FFT functions. These functions seem to take N samples...

Hello, I am having some questions related to FFT while using inbuilt Matlab or Octave FFT functions. These functions seem to take N samples of the signal that needs to be analyzed. Are there any requirement on the length of the input signal that needs to be fed into. A signal can be made up of many frequencies, so, it is obvious that a signal of N length can have any or all of the follow...

Hi all, I'm running into some problems when using FFTs to interpolate data from coarse grids to finer grids. The operation that I'm doing to...

Hi all, I'm running into some problems when using FFTs to interpolate data from coarse grids to finer grids. The operation that I'm doing to achieve this is: * Forward 3D FFT on coarse grid * Copy data to fine reciprocal space grid vector with zero padding * Backward 3D FFT The backward FFT is therefore of larger size than the forward FFT. Despite using double precision FFTs, I find tha...

Hi, I'm starting to learn DSP (Matlab )and I have two questions about it, maybe someone can help me out? I'm trying to measure a frequency...

Hi, I'm starting to learn DSP (Matlab )and I have two questions about it, maybe someone can help me out? I'm trying to measure a frequency from an Audio Device and I'm using FFT to transform it from the time domain to the frequency domain. But I am doing a downsample before the FFT. But you can also do it after the FFT. Do you know what would be the most efficient (before or after)? And why?...

For starters, pardon my simplicity. That said, given - an array of sample data such that: data [ 8 ] = { 0., 0., 1., 0., 2., 0., 3., 0....

For starters, pardon my simplicity. That said, given - an array of sample data such that: data [ 8 ] = { 0., 0., 1., 0., 2., 0., 3., 0. }; If I ran an FFT on that via matlab - so now: a = [0+0i 1+0i 2+0i, 3+0i] b= fft( a ); The result: 6.000 -2.000 - 2.000i -2.000 -2.000 + 2.00i I'm going through a matlab couse and the individual who's teaching the course happens to ...

I'm working with a motorola's DSP56824. But I need a library or algorithm to calculate de FFT (256 points and 1 Dimension). The problem is that...

I'm working with a motorola's DSP56824. But I need a library or algorithm to calculate de FFT (256 points and 1 Dimension). The problem is that I'm working with codewarrior(to programm with C), but I tried to compile some algorithms but they doesn't compile. Someone knows a link for a free FFT algorithm por DSP. Than You

I am new to FFT but after reading, all FFT starts butterfly operation during the middle of the frame. For example, a radix-2, it starts until...

I am new to FFT but after reading, all FFT starts butterfly operation during the middle of the frame. For example, a radix-2, it starts until N/2 sample has been read in from ADC, i.e. but(0, N/2-1), but(1, N/2), ... Is it possible to design it in such a way it performs a butterfly operation real time every two samples? but(0, 1), but(2, 3), ...

Hi all, I have the following problem: a snapshot of a signl s[n], n=0.....N-1. I compute signal power like this: P=1/n*sum(abs(s[n])^2)...

Hi all, I have the following problem: a snapshot of a signl s[n], n=0.....N-1. I compute signal power like this: P=1/n*sum(abs(s[n])^2) n=0,...,N-1. After this I make S=fft(s) and P'=sum(abs(S)^2). Missing out a normalization parameter (depending from fft definition) I have the same result. Suppose noe that I want to use a window function with fft like hanning (for example) my n...

Hello everyone. Have an interesting problem. I have an FFT of an audio signal and I want to interpolate the bins into another frequency...

Hello everyone. Have an interesting problem. I have an FFT of an audio signal and I want to interpolate the bins into another frequency set... instead of a linear set of frequencies, I'd like the frequencies I get (in the end) to be based on an exponential/logarithmic formula, based on the twelfth root of 2... What I'd like to do is take the FFT results and re-interpolate (or re-sc...

Hi, first off I'm fairly new to DSP. That said, here is my situation. 1.I have an input array of time domain samples. 2.I feed this array into...

Hi, first off I'm fairly new to DSP. That said, here is my situation. 1.I have an input array of time domain samples. 2.I feed this array into a FFT, then do an inverse FFT. 3.From the inverse results, I extract the "real" component. 4.I plug the iFFT real components into a new array. Here is output from my program looking at one data sample: time domain sample: -256.0 fft of sample: ...

Hi, appreciate if someone can explain to me why is it when i do a FFT the output spectra is symmetrical? Is this to do with the formulae we used?...

Hi, appreciate if someone can explain to me why is it when i do a FFT the output spectra is symmetrical? Is this to do with the formulae we used? Thanks.

Hello all, There is one factor that seems to be missing from texts which describe the DFT/FFT (or perhaps I have missed it). That is: The...

Hello all, There is one factor that seems to be missing from texts which describe the DFT/FFT (or perhaps I have missed it). That is: The correlation between time domain signal amplitude and frequency domain bin magnitudes. On the one hand, many DSP libraries are very meticulous about documenting the differences between their FFT or IFFT implementation results versus Matlab. For ex...

Hello, while working daily with FFTs, I seem to have forgotten some of my theory :( Given: - the "usual" FFT algorithm that turns N...

Hello, while working daily with FFTs, I seem to have forgotten some of my theory :( Given: - the "usual" FFT algorithm that turns N complex samples in time domain to N complex samples in frequency domain. - a real valued input signal (= some sampled data, sampling rate "fa"). If a is the result of the FFT, there are two "interesting" elements of a: a[0] : This is the DC part ...

Hello all! I'm new on this group. I started following it because I need help for project I'm working on at my faculty. I need to include...

Hello all! I'm new on this group. I started following it because I need help for project I'm working on at my faculty. I need to include an FFT algorithm in my project in order to manage sound signal. Can anyone recommend me a good implementation of FFT in JAVA, because, as I have read about it, there is many of implementations which are not optimised. Code examples about mnaging sou...

Hi all! For the 2048 point FFT implementation I have used two 1024 point Radix-4 (Decimation-in-frequency) FFT and for final stage I have used...

Hi all! For the 2048 point FFT implementation I have used two 1024 point Radix-4 (Decimation-in-frequency) FFT and for final stage I have used 2048 point (Decimation-in-time) Radix-2 FFT. But outputs are incorrect. When input is a pulse at x[i] = {1 when i = 1, 0 otherwise} the real part of output is cosine with frequency = 2, since I have expected the cosine with frequency = 1. Likewise fo...

Im trying to get a feel for when Taking the FFT and doing frequency domain processing is more computationally efficient than doing...

Im trying to get a feel for when Taking the FFT and doing frequency domain processing is more computationally efficient than doing discrete convolution. Does anyone have any specific examples? I understand that very long FIR filtering may have a beneifit if filter is done via FFT then IFFT. Is most real time filtering done in the time domain?

Hi All, I'm trying to understand the differences between FFT and DCT and was hoping someone may be able to help me with a couple of...

Hi All, I'm trying to understand the differences between FFT and DCT and was hoping someone may be able to help me with a couple of questions. 1. Is DCT basically the same as an FFT that operates on real numbers? 2. I keep reading about 'real-odd' and 'real-even'. What does this mean? 3. The fftw documentation also talks about being 'shifted by half a sample'. If by sample it's ta...

Dear All, Can someone describe the algorithm for performing correlation analysis between two signals using fft. I tried using the simple...

Dear All, Can someone describe the algorithm for performing correlation analysis between two signals using fft. I tried using the simple correlation algorithm but as my signals are quite long (upto 45 seconds of audio), as you can imagine, the calculation takes for ever. I know there is a quicker technique to do this by transforming the signals into frequency spectrum using fft, but I am...

Hi all, I am trying to compute the FFT of signal using the integer FFT method. In this I am able to represent the twiddle factors in sum of...

Hi all, I am trying to compute the FFT of signal using the integer FFT method. In this I am able to represent the twiddle factors in sum of powers of two, to do the multiplication operations using the shift and addition operations. Example how to multiply 0.7071 with 0.255 using shift and addition operators only by representing the data in binary form. But the thing is I am not able to ...

Hi! For my little project i need to fft large data arrays, that do not fit into memory. So far i know about overlap add and for some problems...

Hi! For my little project i need to fft large data arrays, that do not fit into memory. So far i know about overlap add and for some problems that works fine, but I wondered if it's possible to transform the whole data altogether. I tried to code a special memory management for the fft but due to bit reversed addressing i get so many page faults that it's really not efficient... I a...

I am new to FFT, but I found that if input is from ADC, the FFT can only start when half of the data is read in (Assume 1024 point, it...

I am new to FFT, but I found that if input is from ADC, the FFT can only start when half of the data is read in (Assume 1024 point, it starts when 511st is sampled, i.e. Butter(0, 511), Butter(1, 512), Butter(2, 513), Is it possible to decompose the sequence to allow Rad-2 butterfly operations as early as possible, say Butter(0, 1), Butter(2, 3), Butter(4, 5), .. ?