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## Re: I Need Help..

**From**: |
Mike Miller |

**Subject**: |
Re: I Need Help.. |

**Date**: |
Fri, 22 Nov 2013 13:14:29 -0500 |

On Fri, Nov 22, 2013 at 17:09:19 +0000, Damian Harty wrote:
>* Unresolved for me is*
>
>* 1) Why only use the real part of the results?*
Assuming the original signal is real, taking the real part of the
inverse FFT and multiplying by 2 is essentially restoring the spectral
symmetry of the FFT. Basically because the low-pass filtering should
have preserved the 8 conjugate-symmetric bins at the end of the array.
>* 2) Why use the DC part from another signal?*
I'm also not sure, without context of what the ec signal is, but it's
essentially subtracting the mean of ec from the low-pass filtered
original_data, right?
Back to the original question, the cutoff frequency of your low-pass
filtering depends on the size of original_data. If L =
length(original_data), then the frequency axis is in units of Fs/L and
the cutoff frequency is 9*Fs/L.
--
mike