Signal abstractions in signal processing software

The authors propose and formally define the concept of multilevel signal abstractions as an organizational principle for real-world signal processing software that requires both algorithmic and heuristic techniques. As an example, they have implemented a set of signal abstractions, the extended spectrum, for harmonic spectra. The extended spectrum is shown to be useful in a variety of problems associated with harmonic spectra. For example, the focus in spectral estimation is often on adjusting parameters to maximize the `peakness´ of harmonically related peaks. It is demonstrated that this can be conveniently performed by taking advantage of the multiple abstraction levels of the extended spectrum representation. The extended spectrum can also be used to represent explicitly the evolution of harmonic spectra over time. To illustrate this concept, the authors have implemented a helicopter pitch and power tracking system