## Forums Search for: FFT

## FFT processor - some issues

ini am working on a FFT processor. i need to know that if i need to take the 1024 point FFT of a voltage time series then what should i do. i...

i am working on a FFT processor. i need to know that if i need to take the 1024 point FFT of a voltage time series then what should i do. i mean which one is correct way. 1) wait for 1024 samples and take their FFT. then wait for another 1024 samples and take their FFT and so on.... 2) wait for 1024 samples for the first time only and take their FFT. then after the computation of this FFT, i...

## Getting better FFT resolution in lowend by downsampling?

inHi, just a little idea that came in my seriously distorted mind :), hopefully it's not a complete nonsense. When analysing audio signals, we...

Hi, just a little idea that came in my seriously distorted mind :), hopefully it's not a complete nonsense. When analysing audio signals, we like log domain, so Q transform, but AFAIK it hasn't been implemented fast enough yet, right? So I thought we can just use FFT and then use another FFT specifically for low-frequencies. Example: SR 44kHz, nyquist 22kHz, FFT 8192, resolution 22000/409...

## Large FFT on ADSP-21065L

inHi. I want to use a very large FFT (65536 samples) on a Sharc 21065L. But I encountered a problem with the ADI FFT (rfft65536) with my DSP:...

Hi. I want to use a very large FFT (65536 samples) on a Sharc 21065L. But I encountered a problem with the ADI FFT (rfft65536) with my DSP: the twiddle-factors need to be in the PM, but that is far too much data for the internal memory of the 21065. I tried the FFT from "Numerical Recipies in C", but the results are not really correct, there are errors for low frequencies. Now I'm looking for...

## FFT on dsPIC33F

inHi, Can anyone help with this ? :- I am using the fft function on the dsPIC from the Microchip library. When I do a fft I get a non...

Hi, Can anyone help with this ? :- I am using the fft function on the dsPIC from the Microchip library. When I do a fft I get a non linear result. The dsPIC function claims the result will be 1/N where N=fft size. When I do a 512 fft with a 20Hz sine signal sampled at 640Hz - I can extract the frequency = 20Hz I dont see how the result is scaled relative to the original signal ampli...

## noise reduction with long fft's

inThere's a statement in Smiths The Scientist and Engineer's Guide to Digital Signal Processing about the effect of fft length on noise. In arguing...

There's a statement in Smiths The Scientist and Engineer's Guide to Digital Signal Processing about the effect of fft length on noise. In arguing the virtues of averaging multiple short fft's instead of one long fft he says "Longer DFTs provide better frequency resolution, but the same noise level." But thats not true is it? The noise level of an fft rises with the sqrt(N). The signal grows wit...

## Zero padded FFt

inHi, In order to increase resolution of my FFT (reduce midbin loss), I want to use a 2N point FFT, N is a power of 2, last N points are...

Hi, In order to increase resolution of my FFT (reduce midbin loss), I want to use a 2N point FFT, N is a power of 2, last N points are zeroes. What is the efficient way to compute this? TIA BRMADHUKAR

## FFT SIZE DETECTION

inDear members, I am encountering a peculiar problem, wherein i have to dynamically detect size of the FFT of the signal...

Dear members, I am encountering a peculiar problem, wherein i have to dynamically detect size of the FFT of the signal taken. for example a signal is taken and fft of it is taken, it may be 128 or 256 or any size. utimately i dont have any iota of knowledge of the signal nor length of the fft taken. i have to dynamically detect the size of fft taken. please do he...

## FFT bins: how do they exactly relate to frequency?

inHi everybody, I am Richard and I am new to this news group, new to dsp and fft. And of course I have a question... I have coded an fft...

Hi everybody, I am Richard and I am new to this news group, new to dsp and fft. And of course I have a question... I have coded an fft and now I'm not sure how the frequency in hz relates to the bin index and the space between the bins. Lets assume I have taken N=1024 samples from an ADC at fs=256khz. Further I have calculated the fft and its magnitude spectrum containing 512 bins....

## FFT: Zero-padding, Windowing - What order?

inHi, I have a question regarding FFT: If I want to calculate the FFT of a signal I would extend the signal to the next power-of-2 length to...

Hi, I have a question regarding FFT: If I want to calculate the FFT of a signal I would extend the signal to the next power-of-2 length to exploit the properties of the FFT. This is done using a simple zero-padding. If I window my signal to reduce leakage, when should this be done? Before or after the zero-padding? Thanks! Kind regards Marc

## replace zeroes with red noise before 2D FFT?

inI came across a claim in another forum for dealing with 2D FFT where there are dead traces (data is t-x domain before FFT). So if there is a...

I came across a claim in another forum for dealing with 2D FFT where there are dead traces (data is t-x domain before FFT). So if there is a dead channel, fill it with red noise whose amplitude matches roughly the other channels, then do the 2D FFT. Supposedly this minimises artefacts. Plausible?

## normalised cross correlation by fft

inHi, I have got a problem doing 2D normalised cross correlation by FFT. The normal 2D cross correlation seems very time consuming for long...

Hi, I have got a problem doing 2D normalised cross correlation by FFT. The normal 2D cross correlation seems very time consuming for long signal so I tried to use FFT. I can now get the equal result of cross correlation both by equation and by FFT, but I can not do the normalisation to get the result of FFT equals to the "normxcorr2" from matlab function. Thanks, Sangthong

## Complex Multiplication and convolution with FFTW

inHi! I am currently use FFTW to compute a two dimentional DFT of real data, I readed the FFTW documentation an proced as follow: /*** The fft.h...

Hi! I am currently use FFTW to compute a two dimentional DFT of real data, I readed the FFTW documentation an proced as follow: /*** The fft.h file *** #include using namespace std; class fft { public: fft(); fft(int rows, int cols); ~fft(); fftw_complex * forward(double *); double * backward(fftw_complex *); fftw_complex * multiply(fftw_complex *, fftw_c

## dc component in fft query

inHi all, Just wondering about the dc component of an fft. If I have an input signal e.g a single cosine wave. When I sample it for say a 128...

Hi all, Just wondering about the dc component of an fft. If I have an input signal e.g a single cosine wave. When I sample it for say a 128 point fft, should it have a dc component value. In my fft, I sum the input samples and calculate the average. I half expected it to be zero (no dc component), but this wasn't the case. Can anyone shed some light upon this ? If the dc componen...

## Some thoughts on I/Q processing

inI have been analyzing a system that has data that is formated in IQ. This data is used to feed an FFT. The data rate of the FFT is 25 KHz and...

I have been analyzing a system that has data that is formated in IQ. This data is used to feed an FFT. The data rate of the FFT is 25 KHz and the FFT has 64 points. I have spent a fair amount of time thinking about a real data stream entering an FFT and I know that when you enter a real data stream into a 64 pt. FFT at 25 KHz that you will get 64 complex spectral lines. These 64 lines for...

## 32-Bit FFT

ini am using ADSP-BF533 EZ-Lite I need a 32-Bit FFT for 24-Bit ADC written in ASM. A own FFT written in C is probably not fast...

i am using ADSP-BF533 EZ-Lite I need a 32-Bit FFT for 24-Bit ADC written in ASM. A own FFT written in C is probably not fast enough. I've found only different 16-Bit FFT's in the Libs. Thx for Help.

## FFT code?

inHi there, i googled myself silly on info on a 2D FFT an Inverse-FFT algorithm. all i find is the math equations. No practical info on how to...

Hi there, i googled myself silly on info on a 2D FFT an Inverse-FFT algorithm. all i find is the math equations. No practical info on how to implement it. Does anybody have some info on implementing an FFT algorithm preferably in VC++.NET ( managed C++) or some clear pseudo code on what steps to take? Thanx Oof

## FFT tricks for optimized multichannel processing

inI'm trying to understand whether it is possible to process multiple, unrelated signals with a single pass of the FFT. There is the very common...

I'm trying to understand whether it is possible to process multiple, unrelated signals with a single pass of the FFT. There is the very common trick mentioned in most DSP texts to speed up the calculation of the FFT for Real data, by just shoving the audio data into the Real and Imaginary parts of the FFT inputs and then calculating as if there were half as many samples. Even though the Imagina...

## FFT calculation problem using TMS320C6416

Hello to all , I am pretty new to this subject so please bare with me ..I am just trying to do a basic FFT calculation code using the Code...

Hello to all , I am pretty new to this subject so please bare with me ..I am just trying to do a basic FFT calculation code using the Code Composer Studio (CCS v5) my goal is to see the number of clock cycles to compute a Radix-2 FFT; the input is a 256 points sine wave, now if i try to see the FFT magnitude which is supposed to be a dirac impulse, the plot comes out to be random..i'll put my ...

## how to do IFFT using only FFT?

inHi all, Suppose we are only given the function for FFT, but we don't have IFFT routine... and we have a real input data squence...

Hi all, Suppose we are only given the function for FFT, but we don't have IFFT routine... and we have a real input data squence x, y=fft(x), now how to use FFT only to obtain the x=ifft(y)? -------------------------------------- What if the input data sequence x is complex-valued? Thanks alot

## FFT Beamforming

inHi, Im an undergraduate student and I have researched how to estimate the direction of arrival of a signal using a FFT. I understand how to use...

Hi, Im an undergraduate student and I have researched how to estimate the direction of arrival of a signal using a FFT. I understand how to use it and how to implement the algorithm, but im unsure as to why when performing an FFT on spatially separated data this yields an angle? Thanks, Jan