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Buzzing sound with FFT

Question asked by Wiklund on Jan 4, 2012

I'd asked something about this earlier regarding the BF518, but I now realize my problem is more general than this.  I have an audio processing application that reads in a frame of stereo audio data, and then performs some processing on it (including a set of fft/ifft pairs).  The problem is that when the ffts (rfft_fr32) are called, a loud buzzing sound is generated.  Regarding this I have made the following observations:


1)The "buzz" is generated in the *input* vector, which is the data that has been read in, rather than added in during processing.  Calling the fft results in an interference sound being added even before actual processing has occured!  Removing the calls to the ffts eliminates this noise.


2)Eliminating the ffts and replacing them with an equivalent or greater delay removes the buzzing sound.  This indicates to me that the problem is not directly related to timing.  The overall processing time is also well below the maximum allowable processing time for the frame.


3)The waveform is shown in the figure below.  In this example, no signal is present, and the frame sizes are 128 samples.