The range of frequency that is possible for the ear to detect. This frequency refers to how many cycles per second a sound wave travels. Higher frequencies (faster signals) mean a higher pitch (note on a scale) and low frequencies (slower signals), create low pitch (deep note) sounds. Anything faster (higher note) or slower (lower note) than what the ear is designed to detect will not be heard. This is different from loudness, or strength of the signal, which can vary no matter the frequency being emitted.