Hyperstable adaptive line enhancer for frequency estimation

An adaptive line enhancer is presented that is based on a resonator-based IIR filter, that uses a hyperstable update to do the adaptation. The main feature of the algorithm is that the strict positive reality (SPR) requirement for convergence associated with the hyperstable update, is satisfied by imposing some simple sufficient conditions on the input sinusoidal frequencies, which may be obtained relatively easily, numerically, even for high order cases.