Power Spectral Density

Power spectral density describes how the power of a time-varying signal is distributed across frequency components. It is a foundational tool in signal processing and shows up repeatedly in accessibility technology: in EMG-based input devices, PSD analysis of electrode signals is used to tell which facial muscle contracted despite cross-talk between channels; in speech recognition and hearing-aid processing, PSD-derived features drive the acoustic front-end; in brain-computer interfaces, band-power in specific PSD regions (alpha, beta, mu) is used as a control signal; in fall detection and activity recognition for older users, PSD of accelerometer data distinguishes walking from falling.