## Forums Search for: FFTW

## faster FFTW?

inHello All, I haven't been able to find a similar thread, so pardon me if this has already been addressed. But I was wondering if anyone has...

Hello All, I haven't been able to find a similar thread, so pardon me if this has already been addressed. But I was wondering if anyone has attempted to convert the latest FFTW release to work with integers (taking into account the necessary trig. modifications, later float conversion for proper numerical results, etc.) in order to get faster results when dealing with a real-time data stream...

## FFTW 3.01 and C++

inHi, I hope this is not off topic! I'm trying to make use of the FFTW library (V3.01) but I have some difficulties working out the data...

Hi, I hope this is not off topic! I'm trying to make use of the FFTW library (V3.01) but I have some difficulties working out the data types which comes with the library - and possibly the coding too! Below I have pasted in my current source code which should calculate the FFT of real input data. The input is a sinusoid signal and I'm looking for non-zero data in the output vector bu...

## FFTW 3.01 and C++

Hi, I hope this is not off topic! I'm trying to make use of the FFTW library (V3.01) but I have some difficulties working out the data...

Hi, I hope this is not off topic! I'm trying to make use of the FFTW library (V3.01) but I have some difficulties working out the data types which comes with the library - and possibly the coding too! Below I have pasted in my current source code which should calculate the FFT of real input data. The input is a sinusoid signal and I'm looking for non-zero data in the output vector but all ...

## another FFTW problem

inHi, I am using FFTW to try another test, f(t)=exp(-x), x> =0, the real part of the Fourier transforms should be 1/(1+x^2). I use xmax=1000, and...

Hi, I am using FFTW to try another test, f(t)=exp(-x), x> =0, the real part of the Fourier transforms should be 1/(1+x^2). I use xmax=1000, and xmin=0, let N=8192. I found the results seems shifted upper, every output value is larger than the analytical solution. My code is like this: program test implicit none include "fftw3.f" integer N parameter(N=8192) integer pi pa

## FFTW image processing frequency value question...(ad nauseum)

inHi, I have been using FFTW to do some image processing, including cross correlations, etc. I have found it to be very useful. I've used the...

Hi, I have been using FFTW to do some image processing, including cross correlations, etc. I have found it to be very useful. I've used the r2c/ c2r combination as well as forward and reverse fftw_plan_dft_1d, based on examples I have found online. I have been reading this discussion group that has helped me figure a lot of things out. However, in my latest application, I still seem to be s...

## fft 'n' size

inHi. I'm using fftw in my code for my signal analysis. In fftw (1D), one of the parameters is 'n'. And the document says, "size n can be any...

Hi. I'm using fftw in my code for my signal analysis. In fftw (1D), one of the parameters is 'n'. And the document says, "size n can be any positive integer, but sizes that are products of small factors are transformed most efficiently (although prime sizes still use an O(n log n) algorithm)" What would be the ideal n value? And does "product of small factors" mean multiples of the 'N' whe...

## How Can i use FFTW in Codewarrior ? 【urgent！！】

inThe FFTW works well in my VC++6.0 . But when i try to use it in codewarrior in the same way. i met some problem. first :#include...

The FFTW works well in my VC++6.0 . But when i try to use it in codewarrior in the same way. i met some problem. first :#include "fftw3.h" then copy the three files libfftw.lib libirc.lib libm.lib into the project folder. the program is go as following: ================================= int i=0; double inputsignal[]={1,2,3,1,2,3,1,2}; fftw_complex * outputsignal; fftw_plan fftwplan...

## Using FFTW with blocks of Complex input...

inI am using FFTW 3.0.1 with a C-program I'm developing. My input data consists of a block of complex data for M channels ordered in the following...

I am using FFTW 3.0.1 with a C-program I'm developing. My input data consists of a block of complex data for M channels ordered in the following fashion: input = [ chan1_sample0, chan1_sample1,...,chan1_sampleN-1, chan2_sample0,...,chan2_sampleN-1,...,...,chanM_sample0,...,chanM_sampleN-1] I would like to take advantage of the "Advanced Complex DFT" capability (e.g.-fftw_plan_many_dft()) to...

## Newbie question on FFT

inI feel kinda shameful for asking such a newbie question, cuz even though I read the FFTW manual and other documentation about DFT's, there is...

I feel kinda shameful for asking such a newbie question, cuz even though I read the FFTW manual and other documentation about DFT's, there is one thing I still don't understand When doing a r2r transform (with FFTW), how do i interpret the result array? I have an array of doubles in input that represent a sound, and in the output an array of the same type and size, the problem is that I ...

## FFTW's 4805 array elements lower limit?!?

inI found out something weird today, when computing r2r DFT's with FFTW 3.0.1 in C, it works with arrays with 4806 elements or more, but...

I found out something weird today, when computing r2r DFT's with FFTW 3.0.1 in C, it works with arrays with 4806 elements or more, but stays stuck into an infinite loop if the array has 4805 elements or less. Anyone knows where this strange limit is coming from? Or am I the only one to experience such a bug?

## fftw and dct/idct

inHi, I'm trying to convert a piece of Matlab code to C using the fftw library, but I'm having some troubles with how to handle the Matlab...

Hi, I'm trying to convert a piece of Matlab code to C using the fftw library, but I'm having some troubles with how to handle the Matlab function "idct". I haven't found much documentation about this but I'm assuming it's a type-II dct so I've been using the "FFTW_REDFT01" but I don't get the same results as when I run the script in Matlab. Using google I have found some vague hints that I might ...

## FFTw Forward/Backwards :s

inHello, I'm having some trouble to use FFTw library... I'm using two plans like this: fftw_plan fftw_plan_r2r_1d(SIZE_OF_IN, in, out,...

Hello, I'm having some trouble to use FFTw library... I'm using two plans like this: fftw_plan fftw_plan_r2r_1d(SIZE_OF_IN, in, out, R2HC, FFTW_FORWARD); fftw_plan fftw_plan_r2r_1d(2*SIZE_OF_IN +2, out, originalInput, HC2R, FFTW_BACKWARD); If i'm not wrong, i should be getting, after executing those two plans, the same as 'in' array, in 'originalInput'. But all i get is noise. ...

## FFTW and Correct Result Interpretation

inI'm using FFTW 3.1.1 and VC++ Pro 2005. The input signal is a 27Hz, 16-bit, 2 channel, Fs=44100, fullscale sinewave (using -32768 to 32767...

I'm using FFTW 3.1.1 and VC++ Pro 2005. The input signal is a 27Hz, 16-bit, 2 channel, Fs=44100, fullscale sinewave (using -32768 to 32767 in amplitude which is the size of type-short). No window function used (a blackman is selectable however it leaks outside of the 27Hz bin). Prior to the fftw_execute, I convert all the samples to an amplitude between -1.0..+1.0 by dividing by 32767 and stori...

## Using FFTW to do analysis of a WAV file

inHi, I'm extremely new to DSP, I just read about the FFT for the first time a couple of days ago. :) I wanted to construct a program will add...

Hi, I'm extremely new to DSP, I just read about the FFT for the first time a couple of days ago. :) I wanted to construct a program will add filter effects to a WAV file. No, I'm not interested in a freeware/shareware program, I want to learn how to do this. I found that I would need a FFT and so, I decided to try FFTW. I'm very new to this program, as you can imagine, and I'm trying t...

## fftw in C++

inHi, Sorry if this is not the right forum but, I didn't know who else to turn to. I have a quite simple process. I use FFTW library to take a...

Hi, Sorry if this is not the right forum but, I didn't know who else to turn to. I have a quite simple process. I use FFTW library to take a forward fft of a one dimensional signal and then do some multiplication in freq. domain and then a backward (inverse) fft. (called in a C++ code). I check the result with matlab (as I understand matlab uses the same library). The forward result is...

## Using FFTW3 to calculate an Gaussian

inHello, I am a new user of FFTW, and I am using Fortran. My problem is to try to get the Fourier Transform of a Gaussian function:...

Hello, I am a new user of FFTW, and I am using Fortran. My problem is to try to get the Fourier Transform of a Gaussian function: f(x)=exp(-x**2). The results should be another Gaussian: 1/sqrt(4*pi)*exp(-omega**2/4). I think the out put files should be all real numbers, no imagine parts. the parts doing FFTW in my code: program test implicit none include "fftw3.f" integer ...

## Weird results from FFTW -- banding and large roundoff

inI have been struggling to figure out some strange results from FFTW. I get a angled banding in the DFT and the inverse gives an image that...

I have been struggling to figure out some strange results from FFTW. I get a angled banding in the DFT and the inverse gives an image that looks generally OK except that the signal varies periodically, consistent with those bands, by up to 1% above and below the original image signal. I have put some picture and description here: http://www.mirametrics.com/pub/fftw_strange_results.htm I hav...

## Fftw for TS101.

inWe're students from Saint Petersburg, from Russia. We had ported fftw 2.1.5 on digital signal processor Analog Devices TigerSHARC TS101. C...

We're students from Saint Petersburg, from Russia. We had ported fftw 2.1.5 on digital signal processor Analog Devices TigerSHARC TS101. C compiler for TS101 it's not so good as gcc or Intel C compiler, that is why we have rewritten on the assembler 2, 3, 5, 6 and 12 points transformations, and other transformations aren't included to a code. And now we have got a good line of points with goo...

## FFTW Library - am i using it right??

inhello, i would like to know if i'm doing this right. my program creates a vector of vectors which it then FFTs using the FFTW library. its...

hello, i would like to know if i'm doing this right. my program creates a vector of vectors which it then FFTs using the FFTW library. its written in C++. my full code is shown below. if this is right, the next step would be to correlate this vector with another. anyway, heres my code: ... #include "fftw3.h" using namespace std; typedef vector convert; typedef vector row;

## FFTW: successive real2complex 1-D FFTs fail

inHi everybody, I've been experimenting lately with the great FFTW library in C, and I've just encountered some very strange behavior. I have...

Hi everybody, I've been experimenting lately with the great FFTW library in C, and I've just encountered some very strange behavior. I have a 1024x1024 image (w=1024, h=1024), on which I want to do the following processing: a) Perform 1-D FFTs on every column of the image array b) Perform 1-D FFTs on every row of the same image array c) more computations using the outputs of the two pre...