## Forums Search for: IFFT

## FFT and IFFT problems on the Motorola 56F8323

inHello all, I would REALLY appreciate if someone could help me figure out why my FFT and IFFT arent working on my Motorola chip. The chip...

Hello all, I would REALLY appreciate if someone could help me figure out why my FFT and IFFT arent working on my Motorola chip. The chip has the 56000e core. All Im doing is, taking an array of 16 Fractionals, that represents a sine wave. Im doing an in-place FFT then inverse FFT on it and the results are COMPLETELY off of what I would expect (Id expect the same sine wave back). I...

## need recommendation(s) for FFT algorithm to use

inHi Experts, My application requires taking FFT and IFFT on a REAL array of points, where the array size is fairly large (number of points in...

Hi Experts, My application requires taking FFT and IFFT on a REAL array of points, where the array size is fairly large (number of points in array ranges between 2^20 to 2^27, which is 1M to 140M). Once in the frequency domain, I zero out all bins except for those bins associated with spurs, then IFFT the array back. I'm looking for a recommendation for an algorithm suited for this purpose ...

## why center tone is null in input of IFFT in OFDM systems

inwhy center tone is null in input of IFFT in OFDM systems ? is it for reducing PAPR ...? or to reduce complexity in OFDM receiver ? ...

why center tone is null in input of IFFT in OFDM systems ? is it for reducing PAPR ...? or to reduce complexity in OFDM receiver ? _____________________________ Posted through www.DSPRelated.com

## Comparison between numerical precision in FFT and manual FT: both error plots show very different behavior

inHi, I was hoping someone could help me understand the effects of the numerical precision in Matlab's FFT. I setup a very simple code that perform...

Hi, I was hoping someone could help me understand the effects of the numerical precision in Matlab's FFT. I setup a very simple code that perform the FFT and IFFT and compare my results to an FFT follwoed by a "manual" IFFT, I see a very strange increasing behavioir in the error and was wondering what this was due to. The fact that it increases with the sample number leads me to believe it's relat...

## oversampling in OFDM

inHi All,, Plz help me for ofdm simulation. I have tried to simulate ofdm signal with 64 subcarriers, with an oversampling of factor 4 in...

Hi All,, Plz help me for ofdm simulation. I have tried to simulate ofdm signal with 64 subcarriers, with an oversampling of factor 4 in frequency domain. Now I've got 256 QPSK symbols with zero paddings.I'm doing IFFT of 256 points. But I need to modulate my data on 64 subcarriers. then how would it be possible if i'm doing IFFT/FFT of 256 points. plz clarify me this thing, if i have zeronpadde...

## IFFT conversion using FFTW libraries

inHi, I am trying to convert a FFT and IFFT Matlab code to C using the fftw libraries. Hoiwever, I am stuck at a particular step: The Matlab...

Hi, I am trying to convert a FFT and IFFT Matlab code to C using the fftw libraries. Hoiwever, I am stuck at a particular step: The Matlab command is: G = ifftn(P21,'symmetric'); ow do I convert this statement to C using the fftw library. I have tried the following steps: 1.I used fftw_plan_dft_2d to compute the FFT for a double array of size nx by ny. the FFT values match the Matlab values. I...

## What is the meaning of complex values in results from an IFFT?

inOK, I understand that when you do an FFT on an array of real values you get an array of complex numbers. Where each complex number represents a...

OK, I understand that when you do an FFT on an array of real values you get an array of complex numbers. Where each complex number represents a frequency wave (sine), the magnitude representing amplitude of the wave and the argument (angle) representing the phase. But when you do an IFFT, what does a complex number represent in the output array? When you are working with IFFTs an

## How to use IFFT to get the system impulse response?

inHello all, I have got the system transfer function of a two port network in frequency domain,the frequency range is from 2Ghz to 12GHz.IFFT is...

Hello all, I have got the system transfer function of a two port network in frequency domain,the frequency range is from 2Ghz to 12GHz.IFFT is used to get the time domain impulse response,but the result is complex ,not real.The impulse response of a system should be real.So,please give me some suggestions.thanks .

## ifft after modifying a signal

inHi I have a signal in the time domain, and I need to perform some changes in the spectrum of magnitude of such signal, and then I want to...

Hi I have a signal in the time domain, and I need to perform some changes in the spectrum of magnitude of such signal, and then I want to reconstruct the signal and take it to the time domain again. The problem I have is that i cannot get the signal in the time domain after the modifications. When I take ifft, I get a vector of complex numbers, and I expect a vector or real numbers. The code I ...

## Is autocorrelation of real sequences an homomorphic system?

inI am working over estimation of fundamental frequency and spectral shift estimation, using autocorrelations and cepstral analysis. The Cepstral...

I am working over estimation of fundamental frequency and spectral shift estimation, using autocorrelations and cepstral analysis. The Cepstral analysis is an homomorphic system, is possible to calculate as: X(w) = FFT[ x(n) ] c(n) = IFFT[ log |X(w)| ] The autocorrelation function is possible to calculate as: X(w) = FFT[ x(n) ] r(n) = IFFT[ |X(w)|^2 ] Note that different is only l...

## ofdm simulation (BER Vs SNR )

inhi i am using this code for simulation of ofdm clear all; Fd=1; % symbol rate (1Hz) Fs=1*Fd; % number of sample per...

hi i am using this code for simulation of ofdm clear all; Fd=1; % symbol rate (1Hz) Fs=1*Fd; % number of sample per symbol M=4; % kind(range) of symbol (0,1,2,3) Ndata=128; % all transmitted data symbol Sdata=8; % 8 data symbol per frame to ifft Slen=16; % 16 length symbol for IFFT X=zeros(Ndata,1); Y1=zeros(Ndata,1); Y2=...

## Frequency response to time domain - lack of understanding!

inHi all, I'm having a few problems with the basics of IFFT. I have created a frequency repsonse (which is an acoustical model of the response of...

Hi all, I'm having a few problems with the basics of IFFT. I have created a frequency repsonse (which is an acoustical model of the response of a room). I want to convolve this with an audio file - thereby making the audio sound like it was played in the room. However, I'm having problems with the IFFT and time domain issues. My frequency response is originally 600 points long, representing ...

## what is IFFT (inverse FFT) equation. And how to derive it from FFT equation?

inwhat is IFFT (inverse FFT) equation. And how to derive it from FFT equation? Is FFT equation same as DFT equation which is X(k)=...

what is IFFT (inverse FFT) equation. And how to derive it from FFT equation? Is FFT equation same as DFT equation which is X(k)= ? x(n)e^(-j*2*pi*k*n/N) ? is from k=0 to N-1 ???? and what is equation for IDFT and IFFT?

## Xilinx FFT core's IFFT function not working? Dun Xilinx TEST their cores before releasing them?

inHi, has anybody used the FFT v4.1 core from Xilinx Core generator before to do IFFT? This is the scenario: - I am using this config of the...

Hi, has anybody used the FFT v4.1 core from Xilinx Core generator before to do IFFT? This is the scenario: - I am using this config of the FFT core with the selected configurations -pipelined, streaming -unscaled. input wave is 24 bits. output is 34 bits. coefficients also 24 bits input 1) I use matlab to generate 24 bit complex waveform and save it into text file 2) I run my...

## Questions about IFFT!

inHi, I am a newbie in DSP. I am trying to get the impulse response of a Channel model, the channel model is in frequency domain(please see...

Hi, I am a newbie in DSP. I am trying to get the impulse response of a Channel model, the channel model is in frequency domain(please see below) k_z(m)=(m-1/2)*pi/D;% k sub z k_r(m)=sqrt((2*pi*F(f)/c)^2-(k_z(m))^2); H=besselj(0,k_r(m)*r)+j*bessely(0,k_r(m)*r); Channel(f)=Channel(f)+(i/(2*D))*sin(k_z(m)*z_s)*sin(k_z(m)*z)*H; My question is when I did ifft to this channel model, the imagin...

## looking for FFT/IFFT core for FPGA

inI'm trying to find a 64-point FFT/IFFT core. Target is Actel IGLOO FPGA family. Needs to run fast enough to complete in 3.2us, which is tough in...

I'm trying to find a 64-point FFT/IFFT core. Target is Actel IGLOO FPGA family. Needs to run fast enough to complete in 3.2us, which is tough in an IGLOO. Actel has a free FFT core but it is not quite fast enough. It's a radix-2 core, which is not optimal for this application. Radix-4 would be better. I've looked at the cfft core on Opencores and it may work for us, but also want to c...

## How to cross-correlate in polar coordinate using FFT?

inHi, We all know the FFT-based cross-correlation in cartesian coordinate is given by: C = IFFT[ FFT[ f(x,y) ] * Conj[ FFT[ h(x,y) ]...

Hi, We all know the FFT-based cross-correlation in cartesian coordinate is given by: C = IFFT[ FFT[ f(x,y) ] * Conj[ FFT[ h(x,y) ] ] Here is the question: how is it possible to do this in polar? I do not think if this is the answer: C = IFFT[ FFT[ f(r,p) ] * Conj[ FFT[ h(r,p) ] ] where f(r,p) and h(r,p) are the polar transformation of f(x,y) and h(x,y).

## IFFT to Wavetable ?

inHi guys, I'm trying to implement an algorithm where you fill in real and imaginary arrays then do an Inverse FFT to convert them to a...

Hi guys, I'm trying to implement an algorithm where you fill in real and imaginary arrays then do an Inverse FFT to convert them to a wavetable. The code I'm basing it from is like this: double real[4]; double imag[4]; // fill them in double wavetable[8]; IFFT(real,imag,wavetable); It's using an FFT library (in a DLL) so I don't know what's going on. The thing I don't und...

## How do I perfrom the correct overlap after FFT/iFFT when using a Blackman window?

inHi, I have a simple application which - continously ready samples at 96kHt sampling rate, - chops it into blocks of, let's say, 16384...

Hi, I have a simple application which - continously ready samples at 96kHt sampling rate, - chops it into blocks of, let's say, 16384 samples, - multiplies each block with the Hann window function, - performs a 16384 point FFT (real-> complex) on each block, - modifies the data (the frequency spectrum) from the FFT, - performs an iFFT (complex-> real) on the data, - shoves it into the outp

## FFT in OFDM and 802.11a

inHi, I have a doubt. May be, someone on this list can help me out here... In IEEE 802.11a (OFDM system), packet data given at end of...

Hi, I have a doubt. May be, someone on this list can help me out here... In IEEE 802.11a (OFDM system), packet data given at end of the standard document (for verification, i assume) can be generated if IFFT-FFT vectors are NOT normalized. unnormalized IFFT vectors have energy = 1/Nfft (Used in transmitter). unnormalized FFT vectors have energy = Nfft (used in receiver). (Nfft-> FFT leng