如何做到真正的逆在FFTW库实时FFT [英] How to do inverse real to real FFT in FFTW library
问题描述
我试图做一些过滤用FFT。我使用r2r_1d计划,我不知道该怎么做逆变换...
I'm trying to do some filtering with FFT. I'm using r2r_1d plan and I have no idea how to do the inverse transform...
void PerformFiltering(double* data, int n)
{
/* FFT */
double* spectrum = new double[n];
fftw_plan plan;
plan = fftw_plan_r2r_1d(n, data, spectrum, FFTW_REDFT00, FFTW_ESTIMATE);
fftw_execute(plan); // signal to spectrum
fftw_destroy_plan(plan);
/* some filtering here */
/* Inverse FFT */
plan = fftw_plan_r2r_1d(n, spectrum, data, FFTW_REDFT00, FFTW_ESTIMATE);
fftw_execute(plan); // spectrum to signal (inverse FFT)
fftw_destroy_plan(plan);
}
我做所有的事情吗?我很困惑,因为在FFTW复杂的DFT的,您可以通过设置这样的标志变换方向:结果
P = fftw_plan_dft_1d(N,IN,OUT,FFTW_FORWARD,FFTW_ESTIMATE);结果
或结果
P = fftw_plan_dft_1d(N,IN,OUT,FFTW_BACKWARD,FFTW_ESTIMATE);
Am I doing all the things right? I'm confused because in FFTW complex DFT's you can set a transform direction by flag like this:
p = fftw_plan_dft_1d(N, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
or
p = fftw_plan_dft_1d(N, in, out, FFTW_BACKWARD, FFTW_ESTIMATE);
推荐答案
HTTP: //www.fftw.org/fftw3_doc/Real_002dto_002dReal-Transform-Kinds.html
http://www.fftw.org/fftw3_doc/1d- Real_002deven-的DFT-_0028DCTs_0029.html
在种指定的方向。
(另请注意,你可能会想除以n来重新规格化你的信号。之后FFTW成倍正常化公约N A变换及其逆。)
(Note also that you'll probably want to renormalize your signal by dividing by n. The normalization convention of FFTW multiplies by n after a transform and its inverse.)
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