Perceptually weighted digital audio level compression

An audio compression filter, implemented at least in part by an audio processing device, for compressing the level of digital audio, the filter comprising:

• a loudness measuring module, wherein the loudness measuring module is configured to determine a measure of loudness of an input audio signal using a perceptually derived filter, and wherein the input audio signal is divided into a plurality of blocks, each block comprising a plurality of samples;
• and
• a compression module, wherein the compression module is configured to:
• determine a target gain amount based at least in part upon a target loudness level and the measure of loudness determined by the loudness measuring module;
• based at least in part on the target gain amount, determine a first linear gain amount using piecewise linear attack/release logic to be applied to samples of a first block of the plurality of blocks;
• based at least in part on the target gain amount and on the first linear gain amount, determining a second linear gain amount using the piecewise linear attack/release logic to be applied to samples of a second block of the plurality of blocks, wherein the first linear gain amount is different from the second linear gain amount and wherein both the first linear gain amount and the second linear gain amount are applied to the respective blocks during one of either an attack phase or a release phase;
• and
• adjust the input audio signal by the first and the second linear gain amounts to produce an output audio signal;
• wherein the loudness measuring module and the compression module use integer calculations.

A method for compressing the level of digital audio using integer calculations, the method comprising:

• receiving an input audio signal that is divided into a plurality of blocks, each block comprising a plurality of samples;
• determining, using integer calculations, a measure of loudness of the input audio signal using a perceptually derived filter, wherein the perceptually derived filter is derived from an approximation of human ear canal resonance;
• determining, using integer calculations, a target gain amount based at least in part upon a target loudness level and the measure of loudness, wherein the determining the target gain amount comprises calculating a ratio of the target loudness level and the measure of loudness;
• based at least in part on the target gain amount, determining, using integer calculations, a first linear gain amount using piecewise linear attack/release logic to be applied to samples of a first block of the plurality of blocks;
• based at least in part on the target gain amount and on the first linear gain amount, determining using integer calculations, a second linear gain amount using the piecewise linear attack/release logic to be applied to samples of a second block of the plurality of blocks, wherein the first linear gain amount is different from the second linear gain amount and wherein both the first linear gain amount and the second linear gain amount are as applied to the respective blocks during one of either an attack phase or a release phase;
• and
• producing an output audio signal by adjusting the input audio signal by the first and the second linear gain amounts.