## Forums Search for: FFT

## FFT and Decibels

inI would like to have a amplitude as well as a decibel display in my program of 16-bit stereo audio. 1) First I take the data from both...

I would like to have a amplitude as well as a decibel display in my program of 16-bit stereo audio. 1) First I take the data from both channels as L,R,L,R,etc and feed it into the FFT as one signal. 2) Next I seperate the FFT data into alternating left and right channels. For example Right = FFT[0], FFT[2], FFT[4]; Left = FFT[1], FFT[3], FFT[5]; 3) I take the left channel and perfor...

## FFT coding help

inHi, I've just coded an easy fft program. You can find it here: http://rapidshare.com/files/147982232/fft.tar.gz.html Compile it with gcc -lm...

Hi, I've just coded an easy fft program. You can find it here: http://rapidshare.com/files/147982232/fft.tar.gz.html Compile it with gcc -lm -I. fft.c ep.c and then run a.out. As you'll see, it takes about 0.5 seconds to do a length-8192 FFT. I think that's a very bad time. Compared to other fft this is a factor of ~1000. What has to be improved? Thanks, Hugo

## Any FFT trick to do this?

inHello, I don't know if its possible to do this with a FFT block, but I hope someone could shed some light on. So basically I receive a train...

Hello, I don't know if its possible to do this with a FFT block, but I hope someone could shed some light on. So basically I receive a train of pulse, say x(t)=x(0),x(1),x(2),x(3),...,x(7). What I want to do is to perform 2x4-point FFT's in this order: FFT{x(0),x(2),x(4),x(6)}, and; FFT{x(1),x(3),x(5),x(7)}. Now I was wondering if there's anyway I can do this, without waiting for t...

## FFT question

inHi all, I always hear that the computational complexity of FFT is O(NlogN). However I learn that there are many FFT algorithms such...

Hi all, I always hear that the computational complexity of FFT is O(NlogN). However I learn that there are many FFT algorithms such as: Cooley-Tukey FFT algorithm ,Split-radix FFT algorithm ,Prime-factor FFT algorithm ,Bruun's FFT algorithm ,,Rader's FFT algorithm ,Bluestein's FFT algorithm are they have the same computational complexity O(NlogN)?? Thanks

## FFT with TMS320F2812

inI use the TI FFT Library and I have two question : First, in the TI example RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input...

I use the TI FFT Library and I have two question : First, in the TI example RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input samples in Real Part fft.win(&fft); RFFT32_brev(ipcb,ipcb,N); RFFT32_brev(ipcb,ipcb,N);// Input after windowing fft.calc(&fft); fft.split(&fft); fft.mag(&fft); There are 4 times "RFFT32_brev(ipcb,ipcb,N); ", I don't know why ? I deleted the last 3 l...

## FFT of 0s and 1s signal

inHello !! I have to FFT a signal made of 0s and 1s, i.e., my sequence is for example, 0,1,1,0,0,0,0,1,0,1,1,0 ... etc This is a true serie of...

Hello !! I have to FFT a signal made of 0s and 1s, i.e., my sequence is for example, 0,1,1,0,0,0,0,1,0,1,1,0 ... etc This is a true serie of 0s and 1s, not a number, written as binary. I am wondering if someone knows about a FFT algorithm able to handle such a cose. I'm not (far not!) an expert in FFT algorithm, but I can imagine that such a "signal" to FFT should impact the FFT code. ...

## FFT length

inHi. A simple question. Given a signal (17Hz) with noise (from external devices, environment, etc), and, say, 10 secs of data, in order to...

Hi. A simple question. Given a signal (17Hz) with noise (from external devices, environment, etc), and, say, 10 secs of data, in order to extract out the signal, which is better to do: a. take the entire 10 secs of data and do a FFT and see if we could see the 17 Hz sticking out b. take a 1 sec FFT of the signal for every 0.5 sec (FFT at 0-1, FFT at 0.5-1.5, FFT at 1-2, FFT at 1.5-2.5, e...

## FFT code for dsPIC

inHi Has anyone written their own fft function for the dsPIC ? (NOT the supplied library fft). I need a fft for measuring signal in noise and...

Hi Has anyone written their own fft function for the dsPIC ? (NOT the supplied library fft). I need a fft for measuring signal in noise and not being a DSP person would prefer to implement it rather than write it from scratch. The dsPIC library scales the data by 1/N which limits the dynamic range of the fft. I can post scale and run the fft again until I have a usable number - its just ...

## time domain zero padding VS fft interpolation between bins

inHi, Suppose I have N samples and I want to do one N point FFT and a 4N point FFT with zeros padding. Can do get the 4N-FFT by...

Hi, Suppose I have N samples and I want to do one N point FFT and a 4N point FFT with zeros padding. Can do get the 4N-FFT by interpolating the N-FFT? Is there a formula? Is the interpolation fast than just do a zero-padded 4N-FFT? Thanks

## FFT Radix

inI am trying to implement a 128 point FFT. I have 16 8-bit samples aligned and ready for input into the FFT. I would like to know if the terms...

I am trying to implement a 128 point FFT. I have 16 8-bit samples aligned and ready for input into the FFT. I would like to know if the terms "mixed radix fft" and "split radix fft" are considered interchangeable. If not, what is different? Is it possible to use 64 radix 2 butterflys in front of two 64 point radix 4 based fft's? Does this make sense? If it is possible, do I need to reorder...

## phase and magnitude of FFT in TI's F2812

inHi, Im trying to use ti's eZdsp F2812 to perform FFT on a simple sinewave. The FFT libraries provided allow me to extract the magnitude square of...

Hi, Im trying to use ti's eZdsp F2812 to perform FFT on a simple sinewave. The FFT libraries provided allow me to extract the magnitude square of the fft but have no such allowance for the phase. The fft calculations are performed in the "in place computational buffer" and its supposed to hold the values of the fft result afterwards (real in the even positions and imag in the odd). I attempte...

## fft question

inhi, can anyone tell me how to perform 2d fft? what i understood for 2d fft is that for each rows we perform individual fft's and place the...

hi, can anyone tell me how to perform 2d fft? what i understood for 2d fft is that for each rows we perform individual fft's and place the result on the respective rows and similarly for the columns. what i mean is suppose i have an array of 2d data as: 0000 0110 0110 0000 now what i am trying to do is calculate fft (4 point fft instead of 16 point fft) of the first row (0000) and plac...

## fft question

inhi, can anyone tell me how to perform 2d fft? what i understood for 2d fft is that for each rows we perform individual fft's and place the...

hi, can anyone tell me how to perform 2d fft? what i understood for 2d fft is that for each rows we perform individual fft's and place the result on the respective rows and similarly for the columns. what i mean is suppose i have an array of 2d data as: 0000 0110 0110 0000 now what i am trying to do is calculate fft (4 point fft instead of 16 point fft) of the first row (0000) and ...

## Overlapped FFT optimization

inHi Guys, I am doing a 256 point FFT in FPGA on High speed ADC data with a custom FFT core...Now i need to do a 4:1 overlap(64 points for 256...

Hi Guys, I am doing a 256 point FFT in FPGA on High speed ADC data with a custom FFT core...Now i need to do a 4:1 overlap(64 points for 256 FFT) on ADC data...that is first 256 point FFT will be done on sample no 1 to 256, next FFT on sample no 65 to 320 and so on...One solution is to use four such FFT cores to perform the operations..I want to know whether there is any other method/optimizati...

## Strange FFT Behavior in MATLAB

inI think we can all agree that FFT { x*(n) } = X*(N-k), or the FFT of the conj of x(n) is the conj of the reversed version of the FFT of...

I think we can all agree that FFT { x*(n) } = X*(N-k), or the FFT of the conj of x(n) is the conj of the reversed version of the FFT of x(n). But in MATLAB if a= [1+2j 3+4j 5+6j 7+8j] then fft(conj(a)) = [16+20j -8+0j -4-4j 0-8j] and conj(fliplr(fft(a))) = [-8+0j -4-4j 0-8j 16+20j] Any ideas? Another engineer and I spent most of a day looking at the mod...

## FFT for ADC output

inHi, I'm new to DSP and FFT. My question is how to do FFT for ADC digital output code,as FFT algorithms i've seen in Internet always ask for...

Hi, I'm new to DSP and FFT. My question is how to do FFT for ADC digital output code,as FFT algorithms i've seen in Internet always ask for real and imaginary parts input for the FFT algorithm. So what is the input for FFT, if we want to do it for digital codes? Thanks

## Help with the KISS FFT library

inI've been struggling for some time now with implementing the Kiss FFT library in a project I'm working on. I just don't seem to be getting the...

I've been struggling for some time now with implementing the Kiss FFT library in a project I'm working on. I just don't seem to be getting the values I expected out of the fft routine. Let me try to explain what I've been doing: I am trying to compute an FFT with a size of 6500 using the real fft transform. I'm sampling a 60 Hz waveform at 390kHz and attempting to calculate the total ha...

## assemble 2K FFT by 2 times 1K FFT?

inHi folks, I heard about the possibility to obtain higher order FFTs by utilizing lower order FFTs. In fact, this IS the basic idea of FFT as...

Hi folks, I heard about the possibility to obtain higher order FFTs by utilizing lower order FFTs. In fact, this IS the basic idea of FFT as far as i know. But since I am not that deep into the theory of FFT, I have a question to the experts. I want to perform a 2K FFT within FPGA. Now i know, that 2K is just a power of 2 but not of 4, what would enable to use radix-4 and so a complexit...

## KISS FFT version 0.2 now does mixed radix

inFFT libraries don't need to be that complicated. http://sourceforge.net/projects/kissfft/ KISS FFT: A mixed-radix Fast Fourier Transform...

FFT libraries don't need to be that complicated. http://sourceforge.net/projects/kissfft/ KISS FFT: A mixed-radix Fast Fourier Transform based up on the principle, "Keep It Simple, Stupid." There are many great fft libraries already around. Kiss FFT is not trying to be better than any of them. It only attempts to be a reasonably efficient, moderately useful FFT that can use fixed ...

## COnvolution and FFT

inHello, I have a gaussian kernel of size [192,192] to be convoluted with an image of size [512,512] for smoothing. Using the FFT property that...

Hello, I have a gaussian kernel of size [192,192] to be convoluted with an image of size [512,512] for smoothing. Using the FFT property that fft of a convolution is the product of the fft of the individual terms (fft(f(t) * g(t))) = f(w)g(w), i could say that smoothedimage = fftinverse(fft(image) fft(kernel)) the problem i am encountering is this: straightforward convolution is easy b...