## Forums Search for: FFTW

## normalizing fftw in the frequency domain

inHi all, I am currently doing a fftw_2d_r2c and i want to know if I must normalize my datas to get a relevant representation of the real part...

Hi all, I am currently doing a fftw_2d_r2c and i want to know if I must normalize my datas to get a relevant representation of the real part and the imaginary part in the frequency domain. Assuming that i have an image of size nx*ny, I have supposed that I should divide by sqrt(nx*ny), is this right? Greetings, Greg

## Another Matlab fft2 != FFTW

inHello, I have something strange... There is a matrix of 5x5, padded with zeroes to 9x9: Columns 1 through 7 -0.1449 -0.0888 ...

Hello, I have something strange... There is a matrix of 5x5, padded with zeroes to 9x9: Columns 1 through 7 -0.1449 -0.0888 0.0095 -0.0816 0.1081 0 0 0.0013 -0.1255 -0.0517 -0.0423 0.0090 0 0 -0.0156 0.2098 0.2978 -0.1366 -0.1449 0 0 0.0103 0.0943 0.0068 0.0311 -0.0550 0 ...

## swapping realft() for fftw, need help

Hi, I have been refactoring some old SMS code that uses a non-GPL'ed (and probably much slower) fft function from a book called "Numerical...

Hi, I have been refactoring some old SMS code that uses a non-GPL'ed (and probably much slower) fft function from a book called "Numerical Recipes in C." One of the first things I am doing is changing this to use fftw3f... I started by focusing on the resynthesis, which uses the inverse-fft method for synthesizing a bank of sinewaves. But I have run into a brick wall: I thought all would ha...

## FFT Different APIs Returning Different Results

inHi All, I prototyped a piece of code using FFTW and it works great and I'm now trying to port it to the iPhone. The iPhone has it's own DSP...

Hi All, I prototyped a piece of code using FFTW and it works great and I'm now trying to port it to the iPhone. The iPhone has it's own DSP library written by Apple which they say is 5x faster than the best competitor. However, when I pass the same data (exactly) into their routine I get a different result set (though interestingly if I graph the data they look similar). My question i...

## help with r2c

inhi, I am using fftw for doing some stuff. i m trying to do the following but get 0 as output .can someone please tell me where am i going...

hi, I am using fftw for doing some stuff. i m trying to do the following but get 0 as output .can someone please tell me where am i going wrong. ///////////////////////CODE BEGINS HERE///////////////////////////////////// #include #include #include int main() { int N = 256; fftw_complex *out; double **in; fftw_plan p; in = malloc(N*sizeof(double

## FFT library

inDear all, I was wondering whether there was any free C/C++ FFT library with a LGPL or BSD style license, or even a propretary license. There...

Dear all, I was wondering whether there was any free C/C++ FFT library with a LGPL or BSD style license, or even a propretary license. There is of course FFTW but it is GPL and for the project that I am currently working on, I am unfortunately unable to release the source code thus I am unable to use it. Your help would be very much appreciated. Many Thanks RG

## Pitch recognition of a musical note on a smart phone

inHi. With limited resources such as slower CPUs, code size and RAM, how best to detect the pitch of a musical note, similar to what a tuner...

Hi. With limited resources such as slower CPUs, code size and RAM, how best to detect the pitch of a musical note, similar to what a tuner would do? Should I use: - Kiss FFT - FFTW - autocorrelation - zero crossing analysis - octave-spaced filters other? Thank you in advance. -mz

## fftw+openmp in Fortran

inHello, after trying to find out why it doesn't work for several weeks, I finally think I should try to find a solution with your help. Here is...

Hello, after trying to find out why it doesn't work for several weeks, I finally think I should try to find a solution with your help. Here is my problem: We calculate a climate modell, which consists of many array, the size of the array depends on the resolution beeing choosed. MAIN.f: implicit double precision (a-h,o-z) external tend include 'RESOLUTION' .. more va...

## Please verify my "solution" to FFT scale factors

inDear DSP masters!! I'm using the FFTW C library to evaluate some signal processing ideas. As I have Richard Lyons Understanding ... book I...

Dear DSP masters!! I'm using the FFTW C library to evaluate some signal processing ideas. As I have Richard Lyons Understanding ... book I first tried his DFT example of paragraph 3.1.1 in order to check if the FFT results are matching. They did. But I would like to use the FFT to get a correct frequency domain representation, so the outputs must be properly scaled. Note: I'm using the FF...

## 2D discrete hartley transform

inDear Readers, I'm trying (unsuccessfully) to find some C code that can perform a 2D-DHT on real-valued data obtained from a 2D image. Does...

Dear Readers, I'm trying (unsuccessfully) to find some C code that can perform a 2D-DHT on real-valued data obtained from a 2D image. Does anyone have workable code they are willing to share? I've been plugging away with the implementation of fftw_dht in fftw, but I'm finding it more than challenging to sort through their code. Sincerely, Mark -- Mark E. Berres University of Wis...

## FFT algorithm for a logarithmically-sampled time series

inHello, is there a C/C++, Fortran, or Python library for calculating a Fourier Transform of a logarithmically-binned times series?...

Hello, is there a C/C++, Fortran, or Python library for calculating a Fourier Transform of a logarithmically-binned times series? Unfortunately FFTW C-library is only good for uniformly-spaced time series. Thank you! ~Andrei.

## FFTw - Manually regenerating the original signal

inHi! I'm totally new to FT:s (obviosly) and don't know much of the math involved. I have a real input signal (Fs=44100) which I've...

Hi! I'm totally new to FT:s (obviosly) and don't know much of the math involved. I have a real input signal (Fs=44100) which I've transformed to a complex and I was hoping to be able to regenerate the original signal manually - just to get the hang of it. It comes "close" :-) I'm using these fftwl_plans: long double *in; fftwl_complex *out; fftwl_plan plan_forward, plan_backwar...

## Re: fftw and derivative. once again

On Monday, January 10, 2011 1:48:44 PM UTC-5, Fred Marshall wrote: ... > assuming that they both start at t=0, > then > the "filter"...

On Monday, January 10, 2011 1:48:44 PM UTC-5, Fred Marshall wrote: ... > assuming that they both start at t=0, > then > the "filter" introduces a delay of N/2 > and > the output of the filter is transient for N/2 samples > it is in steady state more or less for N samples > is in transient again for N/2 samples. ... What am I missing? The transversal filter than best illustr

## Matlab and FFTW Give Different FFT Result?

inHi, Just for testing purpose, I want to calculate the FFT for a 4x4x2 (3D) matrix. The matrix looks like this: in(:,:,1) = 0 4 ...

Hi, Just for testing purpose, I want to calculate the FFT for a 4x4x2 (3D) matrix. The matrix looks like this: in(:,:,1) = 0 4 8 12 1 5 9 13 2 6 10 14 3 7 11 15 in(:,:,2) = 16 20 24 28 17 21 25 29 18 22 26 30 19 23 27 31 Matlab Result: out(:,:,1) = 1.0e+02 * ...

## problem of advanced fftw using

inHi, In the following program, I use the "func_basic_FFT()" tu compute the fft of vector [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Now I want to...

Hi, In the following program, I use the "func_basic_FFT()" tu compute the fft of vector [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Now I want to use the "func_advanced_fft()" to compute a array (including four vectors) 's fft. The array is displayed as follows: Assume four vectors are A,B,C,D, and the array is [ A[0],B[0],C[0],D[0],A[1],B[1],C[1],D[1],... A[15],B[15],C[15],D [15] ] But the...

## FFT and complex numbers

inHi all, I have been looking at some fft libraries libraries and since DSP is not my main area, there are some things that I am confused about....

Hi all, I have been looking at some fft libraries libraries and since DSP is not my main area, there are some things that I am confused about. I noticed that all major fft libraries, e.g. FFTW & kissfft, use complex data types in which to store both the input and the output of the fourier transform. I was wondering, must this always be the case, or is it possible to just use array of pri...

## decimation and anti-aliasing

inDear all, Thanks for all your replies but I am still a bit confused. Let me try rephrasing my question so that everyone gets a better picture...

Dear all, Thanks for all your replies but I am still a bit confused. Let me try rephrasing my question so that everyone gets a better picture of what I am trying to do. I have a large number (order of 10^13) of discretized data samples. I have to obtain the frequency spectrum of this data so that I can predict minima in the discretized data. I am using the FFTW C library to obtain the Frequency...

## Convolution of symmetric data

inHi All! I have to convolute two sets of symmetric data which are zero centered i.e. c=a*b where for example a=[1 2 3 4 5 4 3 2 1] b=[2...

Hi All! I have to convolute two sets of symmetric data which are zero centered i.e. c=a*b where for example a=[1 2 3 4 5 4 3 2 1] b=[2 4 6 8 10 8 6 4 2] The data may be also odd a=[5 4 3 2 0 -2 -3 -4 -5] etc. etc. I can perform the convolution either by FFT or by direct multiplication. But I want to make use of the odd/even symmetry of the data. If I want to use FFTW, it requi...

## realtime convolution with time-varying filter

inHi, i am new to this newsgroup and relatively new to dsp programming (i have basic theoretical background). For my application im trying to...

Hi, i am new to this newsgroup and relatively new to dsp programming (i have basic theoretical background). For my application im trying to implement i need to realtime convolute an audiostream with a time-varying filter. Is there some opensource or at least free C/C++ library that i can easyly use for that? (im alreay checking http://www.fftw.org/ for my fft needs, but would like a lib ...

## Faster fft on P4 + winxp?

inHello, I am using fftw in a fluid simulation code for doing 1D,2D ffts and cosine transforms associaciated with Chebyshev...

Hello, I am using fftw in a fluid simulation code for doing 1D,2D ffts and cosine transforms associaciated with Chebyshev differentiation. All this is done on a P4 pc with winxp. Code written in C on the dev-C++ IDE i.e. the compiler is gcc. To my surprise, it turns out that the simulation run times are dominated by the ffts (I expected the matrix inversion in the elliptical p...