## Forums Search for: FFTW

## Problem using fftw

inI'm transforming one period of a sawtooth signal: -1, -0.998, -0.996, -0.994, ..., +0.994, +0.996, +0.998. The fftw plan I use is:...

I'm transforming one period of a sawtooth signal: -1, -0.998, -0.996, -0.994, ..., +0.994, +0.996, +0.998. The fftw plan I use is: fftw_plan_dft_r2c_1d(N, in, out, FFTW_ESTIMATE); This is the result that I expect: -0.636sin(x) -0.318sin(2x) -0.212sin(3x) -0.159sin(4x) -0.127sin(5x)... And this is what I get: +0.636sin(x) +0.318sin(2x) +0.212sin(3x) +0.159sin(4x) +0.127sin(5x)... ...

## Using FFTW on 64 bit computer Visual Studio 2008

Has anybody been to compile FFTW either dynamically or statically and use it along with Visual Studio 2008 compiler using a 64 bit build? The...

Has anybody been to compile FFTW either dynamically or statically and use it along with Visual Studio 2008 compiler using a 64 bit build? The below program has errors #include "stdafx.h" #include #include "fftw3.h" #pragma comment(lib,"libfftw.lib"); //#include using namespace std; #define N 100 int _tmain(int argc, _TCHAR* argv[]) { fftw_complex *in

## FFTW: FFT and IFFT of real data - wrong data after IFFT

inHi, I use the FFTW lib to do a FFT and a IFFT of real data. So I declare int len = 32; out1 = (fftw_complex*)...

Hi, I use the FFTW lib to do a FFT and a IFFT of real data. So I declare int len = 32; out1 = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * len); in1 = (double*) malloc(sizeof(double) * len); I initialize the in1 field with 0,1,2,3...len-1 I do the FFT due to the documentation: p_for = fftw_plan_dft_r2c_1d(len, in1, out1, FFTW_FORWARD); fftw_execute(p_for); And now the ...

## fftw equivalent soft ware for digital filters

Good Day, Is there any linux software which can help filter design ? IIR/FIR/analog. Thanks Ahmad

Good Day, Is there any linux software which can help filter design ? IIR/FIR/analog. Thanks Ahmad

## ifft in C/C++

inI have used FFTW for my fourier operations in the past, but is there a inverse fourier transform library of some sort out there that is just...

I have used FFTW for my fourier operations in the past, but is there a inverse fourier transform library of some sort out there that is just as fast?

## 1800Hz Detection

inHi all, i'm new to DSP so consider that before reply me :-) I have PCM data from a Voice Modem and i need to dectect if is a 1800Hz tone. I...

Hi all, i'm new to DSP so consider that before reply me :-) I have PCM data from a Voice Modem and i need to dectect if is a 1800Hz tone. I think that i need to use FFT (fftw, for precision) but i can't be able to understand nothing. Someone can help me with C code example ? Thanks in advance, Oz

## Re: fftw and derivative. once again

On Sunday, January 9, 2011 6:52:09 PM UTC-5, Tim Wescott wrote: ... > You're not using any frequency limiting -- are you sure you're not...

On Sunday, January 9, 2011 6:52:09 PM UTC-5, Tim Wescott wrote: ... > You're not using any frequency limiting -- are you sure you're not just > amplifying the heck out of your noise? > > In Scilab: > > --> N = 4096; n = 0:N-1; > > --> nn = pmodulo(n + N/2, N) - N/2; > > --> x = exp(-nn.^2 / 100000); xd = ifft(fft(x) .* (-nn .^ 2)); > > --> clf; plot2d(n, [x' xd']) > > gives

## fftshift

inHi Need to do fftshift in 3 dimensions using fftw library but can't find it. Does anyone know if there is a function for this in the above...

Hi Need to do fftshift in 3 dimensions using fftw library but can't find it. Does anyone know if there is a function for this in the above library ? Thanks in advance H.

## 2D image processing with FFTW

inHello group, I'm having some trouble getting my code to work correctly using C++ and libfftw (which is, may I remark, absolutely marvellous)....

Hello group, I'm having some trouble getting my code to work correctly using C++ and libfftw (which is, may I remark, absolutely marvellous). Basically I'm FFTing a picture (real to complex) and then performing and IFFT (just to see if everything works as expected). Well, it does not - I'm having some really stupid problem with which I now spent half a day. Can't figure out what I'm doing ...

## Good Wiener filter implementation in C/C++?

inI've been looking for a modern, efficient Wiener filter implementation written in C or C++, and I can't find anything very recent (or one...

I've been looking for a modern, efficient Wiener filter implementation written in C or C++, and I can't find anything very recent (or one that actually works). I'd like one implemented on top of fftw if possible. Anyone got any pointers to one?

## Flicker detection with DFT Problem

inHello Everybody, I'm not very experienced with DFT and FFTW library and I want to ask your opinion about the results I get. My aim is to...

Hello Everybody, I'm not very experienced with DFT and FFTW library and I want to ask your opinion about the results I get. My aim is to determine if the sample input sequence is flickering with some frequency. In my project, I'm capturing frames from a video and geting the mean pixel value of some pixels with a certain property. I get one mean value for each frame. I want to check if these...

## PSOLA -- changes in duration

inHi all! Greetings! I was working on pitching shifting for quite sometime. I used Mr. Bernsee's code for that purpose, modified it to use...

Hi all! Greetings! I was working on pitching shifting for quite sometime. I used Mr. Bernsee's code for that purpose, modified it to use fftw and tweaked a little to bring its response time down, not much but by 7 seconds. But I am still not able to use it for real-time processing. The listing spends 98% of its time performing in-out transforms to frequency domain. So I thought about sw...

## FFT Rounding error?

inI computed this forward FFT using MS VC++ 6.0 and FFTW: http://www.holmea.demon.co.uk/Misc/FFT.gif I don't think the "tail" should flick up...

I computed this forward FFT using MS VC++ 6.0 and FFTW: http://www.holmea.demon.co.uk/Misc/FFT.gif I don't think the "tail" should flick up like that at the low-frequency end. Is this caused by a lack of floating-point precision? TIA

## Seeking Free Frequency analysis toolkit or examples

inHi, I'm currently a 17-year-old student trying to do a project, involving embedding data within an audio file. Hopefully, it will survive...

Hi, I'm currently a 17-year-old student trying to do a project, involving embedding data within an audio file. Hopefully, it will survive MP3 compression... so I've come to the conclusion I will have to convert all the samples to the freq. domain to do any analysis. I downloaded FFTW and I have it working, but it assumes that the user knows what he's doing (which I do not really). I f...

## fftw3.1 static library on win64

Hi, I am trying to locate an appropriate forum to discuss compiling fftw on a 64 bit pc for use with MS Visual Studio 2005. I am able to...

Hi, I am trying to locate an appropriate forum to discuss compiling fftw on a 64 bit pc for use with MS Visual Studio 2005. I am able to build a library after making modifications to config.h but when I run a very simple test program I get memory leaks. If there is any interest, I am willing to post more information. Thank you. Jason

## Re: fftw and derivative. once again

Yes. The -om^2 must be a mistake. Whatever, it's not enough to simply fidoodle the amplitudes. In addition, the phases have to be advanced by 90...

Yes. The -om^2 must be a mistake. Whatever, it's not enough to simply fidoodle the amplitudes. In addition, the phases have to be advanced by 90 degrees, and that implies a different delay for each spectral line. I have an intuitive feel for what the time derivative of a discrete sequence means, but I'm glad that I don't have to deliver a mathematical definition. Jerry

## fftw 1D transform of 2D signal

inHello, I have a 2D signal (x,y) in an array, and I would like to fourier transform it along one and only one dimension, x for example. I...

Hello, I have a 2D signal (x,y) in an array, and I would like to fourier transform it along one and only one dimension, x for example. I have (nx+1) and (ny+1) points in the x and y direction respectively. the data is stored in a 1D array so that the (i,j) point is simply i + j*(nx+1) I think that the advanced interface should be good for my problem, but I don't understand ...

## fftw_plan_dft_1d V.S. fftw_plan_dft_r2c_1d

inhi, I'm using FFTW library for a Convolution Reverb application. Right now I'm using the fftw_plan_dft_1d function to plan my dfts. Later on I...

hi, I'm using FFTW library for a Convolution Reverb application. Right now I'm using the fftw_plan_dft_1d function to plan my dfts. Later on I tried using the fftw_plan_dft_r2c_1d. I was expecting to get the same result, but the results are different. Is my expectation wrong? Or do I have to overlook my code? These are the lines I use for the planning part p1 = fftw_plan_dft_1d(BLOCK_SIZE ...

## DCT derivative

inHi all, I am trying to calculate derivatives of chebyshev coefficients using FFTW for cosine(x). However I am not getting back the right values...

Hi all, I am trying to calculate derivatives of chebyshev coefficients using FFTW for cosine(x). However I am not getting back the right values when I perform inverse chebyshev transform. Can anyone check the code below and tell me the possible errors. Thank you. program test implicit none #include "fftw3.f" INTEGER, PARAMETER :: N=4 INTEGER(8) :: plan ...

## Correlation of 2 Sequences using FFT (W/W.O FFTW)

inHi All, I am very much excited to see that this group answers almost all the doubts. But I have some trivial yet confusing...

Hi All, I am very much excited to see that this group answers almost all the doubts. But I have some trivial yet confusing doubts. Situation/Objective: Correlating 2 Sequences -- S = {s1,s2,s3,...sN} and C = {c1,c2,c3,....cM} where S and C are 2 discrete set of points one of length N and one of length M (say, M> N). We do not know anything about their periodicity or any other propertie