Inverse FFT of real signals | Analog Devices DSPs

Technical discussions related to Analog Devices DSPs (including Blackfin, TigerSHARC, SHARC and ADSP-21xx DSPs).

Hi all, I saw the ADSP-21062_Real_FFT_rad-2.zip for a real FFT implementation on a 21062 processor. I didn't find anything about the inverse FFT algorithm. In the complex implementation (ADSP-21062_Compl_FFT_rad-2.zip) there are some hints to make the inverse transform. Thanks, Fabrizio

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On Wed, 15 Sep 2004, soundbyfabrizio wrote: > Hi all, > > I saw the ADSP-21062_Real_FFT_rad-2.zip for a real FFT implementation > on a 21062 processor. > I didn't find anything about the inverse FFT algorithm. > > In the complex implementation (ADSP-21062_Compl_FFT_rad-2.zip) there > are some hints to make the inverse transform. Works the same way for the real. Your output from the real fft is "half complex" - that means you only need half the data since the negative frequency space is filled with the complex conjugates of the positive freqs anyway. So you perform a "half complex" inverse to get back your real data. Example: input is 1024 words of real data. Perform fft and get 512 freq bins of complex. do a complex->real inverse on 512 complex data to get 1024 real points back. For code see the Gnu Scientific Library and specificly gsl_fft_real_transform(), gsl_fft_halfcomplex_transform(). They have radix 2 versions also. Patience, persistence, truth, Dr. mike

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Discussion Groups | Analog Devices DSPs | Inverse FFT of real signals

Inverse FFT of real signals - soundbyfabrizio - Sep 15 9:29:00 2004

Re: Inverse FFT of real signals - Mike Rosing - Sep 15 13:27:00 2004