1. A system for leveling loudness variation in an audio signal, the system comprising: a first long term loudness leveling processor configured to measure a first actual loudness of the audio signal using a first long term integration time; a first loudness to gain processor configured to calculate a first gain value using a difference between a desired loudness of the audio signal and the first actual loudness of the audio signal; a first audio modification processor configured to modify the audio signal using the first gain value to generate a modified audio signal; a short term loudness leveling processor configured to receive the modified audio signal and the desired loudness, and configured to adjust a short term loudness of the modified audio signal using a short term integration time, to yield an adjusted audio signal, wherein adjusting the short term loudness comprises using spectral analysis and models of human hearing to adjust the modified audio signal; a second long term loudness leveling processor configured to measure a second actual loudness of the adjusted audio signal using a second long term integration time, wherein the second long term integration time is longer than the short term integration time; a second loudness to gain processor configured to calculate a second gain value using a difference between the desired loudness and the actual loudness of the adjusted audio signal; and a second audio modification processor configured to modify the adjusted audio signal using the second gain value.