On Wed, Aug 11, 2004 at 03:53:09 +0200, Alfons Adriaensen wrote: > In general it will not. Consider a simple case: your signal is a cosine > wave with n periods in the FFT length and amplitude 1. When you apply > the raised cosine window, what happens is that two new cosines with > resp. n-1 and n+1 periods per FFT length and amplitude -0.5 are added, > giving of course zero at both ends. > > The same happens with a more complex signal: the amplitudes of all cosine > components are modified so as to make them cancel at the ends. When you > disturb that delicate balance, they will no longer cancel out. > > Now for each group of three adjacent bins, a linear g(f) slope will not > modify the sum of the ampitudes, e.g. it could transform the -0.5, 1, > -0.5 of above into -0.6 1 -0.4, but the sum is still zero. So the > inbalance and the expected signal amplitude at the ends after the IFFT > will be proportional to the second derivative of the frequency response.
OK, thanks, I think I followed that, but I need to think on it harder. BTW, before you mentioned root raised consine windows before and after, I did a bit of googling, and couldn't find much reference to root raised cos in windowing (just pentions in-passing), do you have a reference or the windowing function/attentuaion factor or anything? In the meantime I'l try it with vanilla raised cosines. - Steve