Psychoacoustics based gain compensation for low listening levels

Abstract

Although the human hearing system is very complex and only understood to a limited degree, many measurements and models exist that explain parts of the hearing system. This paper uses one of these models, the contours of equal loudness, along with DSP techniques, to make music played at low listening levels sound more like it does at the intended listening level. The perceived frequency balance of music varies with listening level. This is especially noticeable at low listening levels, where frequencies below 500 Hz seem attenuated. Moreover, hearing perception exhibits nonlinear dynamic range compression, most evident at low frequencies. Traditional methods add fixed low-frequency gain to compensate for perceptual low-frequency attenuation at low levels. These methods do not consider the dynamic range compression and its nonlinearity and are often characterized by a boomy, unnatural sound. A system is designed where filter banks and power measurements estimate the time-varying power of low-frequency parts of the audio signal. The time-varying power of each narrow frequency band is compared to the contours of equal loudness, and changes are made to get the same frequency balance as at the intended listening level. The paper covers the design, implementation and performance of this system.