Psychoacoustics

Psychoacoustics is a branch of psychophysics that studies the perception of sound. It investigates how physical sound waves are transformed into perceptual experiences by the auditory system, and how factors such as level, frequency, spectral content, context, and attention influence what we hear.

Research topics include detection thresholds, loudness, pitch, timbre, and spatial hearing, as well as phenomena such as masking, auditory scene analysis, and binaural interactions. Methods combine controlled listening tests with systematic variation of acoustic stimuli to measure perceptual judgments, discrimination ranges, and perceptual scales.

Key concepts include loudness scales (phon and sone), pitch scales (mel), and equal-loudness contours (the Fletcher–Munson curves). The idea of a critical band describes a bandwidth over which sounds interact perceptually, explaining masking and frequency resolution.

Applications arise in hearing technology, such as hearing aids and cochlear implants, and in audio engineering and consumer sound reproduction, including formats like MP3 and AAC and noise-reduction systems. Psychoacoustic models are used in sound design, virtual reality, and psychoacoustic-based audio compression to reduce data while preserving perceived quality.

History and development: early work by Fechner laid the groundwork for psychophysics, while mid-20th-century researchers such as Fletcher and Munson established practical loudness relations. Later contributions by Zwicker and Fastl formalized critical-band theory and loudness modeling, and contemporary work links perceptual findings to neural coding in the auditory system.