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Audio normalization is the process of increasing (or decreasing) the amplitude (volume) of an audio signal. Typically normalization increases the amplitude of the audio waveform to the maximum level without introducing any distortion into the recording.
Specifically, normalization applies a constant amount of gain to an entire recording to bring the highest peak to a target level, usually 98% (-0.3 dB) or 100% (0 dB). This differs from dynamics compression, which applies varying levels of gain over a recording to fit the level within a minimum and maximum range. Normalization applies the same amount of gain across the entire recording so that the relative dynamics are preserved.
I'm looking for: Normalization requires two passes. The first pass determines the highest peak, and the second pass applies the gain to the entire recording.
Normalization is often used when remastering audio tapes for CD production, in order to maximize the bandwidth on an audio CD, and to make it sound louder. It is often combined with dynamic range compression and hard limiting to increase the apparent volume of a CD. It is typically applied along with other audio and digital processing, such as dithering.