[FFmpeg-devel] [PATCH 1/5] libavcodec: Implementation of 32 bit fixed point FFT

Zeljko Lukac Zeljko.Lukac at imgtec.com
Tue Jul 16 18:09:07 CEST 2013

Hi Mike,

Yes, that is correct. 

Rockbox FFT has accuracy of ~ 25 bits (25.4 ).
Our FFT with the same multiplication as Rockbox FFT has accuracy of ~ 25 bits (25.6).
Our original FFT has accuracy of ~ 28 bits (27.9).

We think that we get can get similar speed performance of our original and modified FFT for optimized code. If for some application less accurate FFT variant is needed both can be provided.

Best regards,

>Hi Zeljko,
>I worked a bit on the Rockbox FFT.  We took the FFMPEG one as-is and adapted it for use on simple ARM devices (our >goal was ARM7/ARM9).  Perhaps on newer, more deeply pipelined devices it is not as efficient.
>One question, how do I interpret the RMSE values?  Is it value/2^31?  So 48.18 would be ~ 25 bits accuracy?  Or am I misunderstanding?

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