{HEAD ~ The Fourier transformed data} is filtered by retaining {TAIL ~ a subset} of the Fourier coefficients at each of the locations 
is filtered by retaining
{ HEAD ~ The Fourier transformed data } is filtered by retaining { TAIL ~ a subset } of the Fourier coefficients at each of the locations
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH