1. An improved method of operating a RADAR or wireless communications signal processing apparatus implemented as either one or more programmable processors or as special purpose logic circuitry for detecting channel-induced and target-induced chirps in a signal or for classifying a target from a signal using spectral feature extraction, the method comprising: operating a spectral feature extracting engine of the apparatus to: remove direct current bias from a RADAR or wireless communication signal captured by a receiver, the signal having impairments including multiplicative and additive noise, in order to produce a bias-free signal; transform the bias-free signal into a time-frequency spectrum; slice the time-frequency spectrum across time into time-frequency slices, each of the time-frequency slices having spectral content representing a measure of power spectral density of the bias-free signal at a given point in time; compute an initial detection threshold associated with the given signal from the time-frequency slices; compare, for at least some of the time-frequency slices the spectral content of a subject time-frequency slice with the computed initial detection threshold to identify an initial detection; determine a spectral detection density as a function of a number of initial detections being identified and number of time-frequency slices being compared; and operating a chirp detecting engine of the apparatus to detect channel-induced and target-induced chirp(s) present in the given signal based on the determined spectral detection density or, a target classifying engine of the apparatus to classify a target from the given signal based on the determined spectral detection density, thereby improving an ability to detect the channel-induced and target-induced chirps in the RADAR or the wireless communication signal impaired with multiplicative and additive noise.