1. A method for processing an audio signal, comprising calculating, in response to the audio signal, a gain value, which when multiplied with the audio signal makes the error between the perceived loudness of the audio signal and a reference loudness level within a threshold, wherein a portion of calculating said gain value is a non-linear process for which no closed form solution for said gain value exists, and wherein the calculating includes deriving from said audio signal an excitation signal divided into a plurality of frequency bands that simulate the excitation pattern along the basilar membrane of the inner ear, deriving from the excitation signal in each frequency band of the excitation signal, in said non-linear process, a specific loudness, and combining the specific loudnesses to obtain the perceived loudness, iteratively adjusting the magnitude of the excitation signal until the error between the perceived loudness and the reference loudness is below said threshold, the iterative adjusting being performed in an iterative loop that includes deriving the specific loudness in each frequency band of the excitation signal and excludes deriving said excitation signal, and adjusting the perceived loudness of the audio signal using the calculated gain value.