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BF547 FFT related questions

Question asked by Andrew.Choi on Jul 5, 2018
Latest reply on Jul 5, 2018 by Jithul_Janardhanan

Hi all

 

One of my customers asked about using the FFT function of BF547.

 

When using FFT function (cfftf, cfftrad4) provided by VDSP ++ Library while implementing FFT with ADSP-BF547 DSP, phase angle error occurs more than 1 degree.

 

FFT function driven environment
   - FFT Point: 32768
   - 50kHz Sine Wave (Sampling Frequency: 16.384MHz)
   - Functions used: cfftf (frac32 Fast Radix-4), cfftrad4 (frac16 Radix-4)

   - using VDSP++ 5.1.2

 

There is no phase error when FFT operation is directly implemented by own C code.

However, the difference between the result of the FFT operation (floating point operation) and the power value derived from the DSP FFT function operation (Fixed Point) provided by the library is large.

 

The customer is wondering whether it is due to the Phaes resolution of the FFT function used or if the function is implemented incorrectly.

 

Can someone point out why this is happening?

 

Regards

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