Most sounds of interest consist of complex, time-dependent admixtures of tones of diverse frequencies and variable amplitudes. Both detection and processing of these signals begin in a highly nonlinear, adaptive, real-time spectral analyzer: the inner ear, or cochlea. This complex organ spatially separates frequencies through position-dependent resonances along its length. It further boosts faint sound and hence its sensitivity through an active process. I present recent theoretical and experimental work on the functional principles of the cochlea, as well as on novel engineering approaches that they can inspire. I then give an overview of the central nervous system’s capability to analyze and attend to auditory signals. The involved cognitive processes may begin within the cochlea and the brainstem as measurable through electroencephalographic (EEG) recordings. Such measurements can aid to diagnose and support patients with central auditory disorder such as resulting from traumatic brain injury.