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# Reflecting negative frequency to positive frequency

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#### mfl

##### Newbie level 3
I am trying to sample the magnitudes of a shifted window in the frequency domain. I seem to be doing it wrong when a part of the window sits in the negative frequency. Does anyone know the correct way of reflecting negative frequency to the positive side?

Here is an example: if the window (a real symmetrical, ie. H[-k] = H[k]) is centered at 80 Hz, and the sampling interval (the interval between two bins) is 43 Hz. These are the bins before and after the center of the window:

Code:
bin[center] : 86 Hz
bin[center - 1]: 43 Hz
bin[center - 2]: 0 Hz
[B]bin[center - 3]: -43 Hz[/B]

bin[center + 1]: 129 Hz
bin[center + 2]: 172 Hz
bin[center + 3]: 215 Hz

The bin[center -3], at the left tail of the window, sits in the negative frequency. I read somewhere saying that the magnitude at bin[center -3] should be added to bin[center + 3] after a complex conjugation. As the complex conjugation is just flipping the sign of the imaginary part, I figure it would just mean to add twice of the real parts of the magnitude of the window at bin[center +3], which appears a bit strange to me. Also I got a very distorted signal with this method. What am I doing wrong? Any advices would be very appreciated!

Cheers,
mf

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