Classical spectral analysis often relies on methods based on (Fast) Fourier Transformation. This technique has no unique solution separating variations in amplitude and frequency. This drawback is circumvented by using a polynomial approach (ACE v.1 model) to estimate instantaneous amplitude and frequency in orbital components. The model is illustrated and validated using a synthetic insolation signal and tested on two case studies: a benthic δ¹⁸O record and a magnetic susceptibility record.