Hello, I'm writing an application where I get the output of the IFFT operation, using the arm_cfft_f32 function from CMSIS-DSP library like this:
arm_cfft_f32(&arm_cfft_sR_f32_len128, out_ifft, 1, 1);
where out_ifft is a 128*2 element vector with Hermitian symmetry because I need a real output.
I prepare the same vector and I use it again in Matlab to check the results:
salidamod=ifft(ifftshift(vector,2),NFFT);
The ifftshift function swaps the left and right halves of the vector,and it's necessary due to the requirements of the Matlab ifft function. I get this results:
Only the even samples are wrong, and only reversed...It's strange and I don't know why it happens. Could someone explain me the reason, please?
Thank you in advance.
I think that it's something inside the algorithm because I get the correct output in both cases when I use the inverse functions (FFT) I assume that it could be the possible answer...
Do you mean you performed a (forward) FFT on the values you tabulated and you recovered your original frequency samples (those that exhibited Hermitian symmetry) both in CMSIS-DSP library and MATLAB?
Some members also encountered problems regarding forward and inverse FFT:
the first one is very similar to yours, the second is about forward FFT.
Yes, exactly. The first case you've showed is similar than mine, but I don't use the Real IFFT, I use the Complex IFFT but I get a real signal at the output because the input has Hermitian Simmetry.
As the receiver in both cases can get the correct values I think that the problem isn't so important. Although, thank you everyone for your help
OK.