Re: I Need Help..

[Mike Miller]

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