TODO: Dedoppler kernel can affect previous spectrum edges

[telegraphic]

In the deoppler kernel, we check for illegal memory accesses by asserting idx > 0 and idx < F * T.

We do not check that the index of the current spectrum 0 < idx_spec < F. This would stop aliasing at the edges, but is not a major issue as it only affects a small number of channels near the edge of the gulp.