The problem of retrieving narrowband or sinusoidal signals in additive noise, colored or white, is considered in this paper. A frequency-domain analysis leads to a notch filter estimator producing unbiased estimates of the sinusoidal frequencies. The notch filter lends itself naturally to a frequency decoupled realization i.e. cascaded form realization. This has desirable numerical consequences which is essential for resolving closely spaced spectral lines. The method also features an adjustable debiasing parameter α whose proper adjustment results in a decent rate of convergence to highly accurate estimates. Based on some frequency-tracking simulations, the method also appears to possess good tracking capability.