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a quantity that characterizes auditory sensations for a given sound. Loudness depends in a complex way on sound pressure (or sound intensity), frequency, and form of vibrations. Where frequency and form of vibrations are constant, loudness increases with an increase in sound pressure. Where sound pressure is the same, the loudness of pure tones (harmonic oscillations) of different frequencies is different—that is, at different frequencies sounds of different intensity can have the same loudness. The loudness of a given frequency is evaluated by comparing it with the loudness of a simple tone of 1.000 hertz (Hz) frequency. The sound pressure level (in decibels [dB]) of a pure tone of 1,000 Hz frequency that is as loud (audially) as the tone being measured is called the loudness level of the given sound (in phons). Loudness for complex sounds is rated on an arbitrary scale in sones. Loudness is an important characteristic of musical sound.