The quadratic form V pϕ, Qq " ř q"Q ř a mod ˚q |Spϕ, a{qq| 2 and its eigenvalues are well understood when Q " op ? N q, while V pϕ, Qq is expected to behave like a Riemann sum when N " opQq. The behavior in the range Q P r ? N , 100N s is still mysterious. In the present work we present a full spectral analysis when Q ě N 7{8 in terms of the eigenvalues of a one-parameter family of nuclear difference operators. We show in particular that (a smoothed version of) the quadratic form V pϕ, Qq may stay away from p6{π 2 qQ ř n |ϕn| 2 when Q -N , though only on a vector space of positive but small dimension.