Exposure to high-level sounds, including music, produces a variety of physiological changes in the auditory system that in turn produce a variety of perceptual effects. Damage to the outer hair cells within the cochlea leads to a loss of sensitivity to weak sounds, loudness recruitment (a more rapid than normal growth of loudness with increasing sound level and a consequent reduced dynamic range), and reduced frequency selectivity. Damage to inner hair cells and/or synapses can lead to degeneration of neurons in the auditory nerve and hence to a reduced flow of information to the brain, even when audiometric thresholds remain normal. This leads generally to poorer auditory discrimination and may contribute especially to reduced sensitivity to the temporal fine structure of sounds and to poor pitch perception. Hearing aids compensate to some extent for the effects of threshold elevation and loudness recruitment by the use of multi-channel amplitude compression, but they do not compensate for reduced frequency selectivity or loss of inner hair cells/synapseseurons. The multi-channel compression processing used in hearing aids can impair some aspects of the perception of music, such as the ability to hear out one instrument or voice from a mixture. The limited frequency range and irregular frequency response of most hearing aids is associated with poor sound quality for music. Finally, systems for reducing acoustic feedback can have undesirable side effects when listening to music.
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