Compressor/Expander

This effect controls dynamic range, the difference between the loudest and softest sounds. For example, if you want to make soft sounds louder, you could increase the gain, but because gain changes the entire clip, you risk making moderately loud sounds in the clip too loud. Instead, use this effect to raise the level of the softest sounds without changing the level of the loudest sounds. This compresses the dynamic range, creating a smaller difference between the softest and loudest sounds. Expansion creates a larger difference, which can emphasize volume differences. For example, to make sounds more percussive or to reduce noise, you can emphasize loud sounds and de-emphasize quiet sounds.

Although you can compress audio to a smaller dynamic range than the original, you cannot expand dynamic range beyond what was originally available in the audio clip. When you expand a portion of the dynamic range--the portion you want to emphasize--the expansion is always acquired at the expense of the remaining original dynamic range.

Ratio Specifies the rate at which the effect is applied as soft sounds get louder. When Compressor is selected, Ratio specifies the expansion ratio to the right of the Threshold, represented by the red line in the graph. When Expander is selected, Ratio specifies the compression ratio to the left of the Threshold.

Threshold Specifies the level at which compression begins or expansion ends, also commonly known as the knee. In the graph, Threshold is represented by the green line.

Gain Specifies the audio level at the Threshold. Adjusting gain affects the overall output level. In the graph, Gain is represented by the red line.

Function Specifies whether you use the effect for compression or expansion.

In the graph, the gray line represents the original dynamic range. If the right end of the red line is above the end of the gray line, more sounds are using the loud end of the dynamic range. If the end of the red line is below the end of the gray line, the loudest sound is not as loud as it was in the original clip.

Applying Effects > Audio effects included with Premiere > Compressor/Expander