Compressor

Blast! I put text in here when I created this page, but must have forgotten to save the preview. Trying again. --James.

Description and Usage

Compressor boosts faint sounds, at the expense of louder sounds. It's particularly useful for audio that will be played in a noisy background, such as in a car stereo. 'Compressing' the louder sounds gives more headroom for amplifying the fainter sounds without causing clipping.

Compressor can also be useful in dialog where one person is speaking more quietly than another - or was further from the microphone.

It works by monitoring the level (related to loudness) of the audio signal, and reducing the gain applied when it exceeds the threshold level. Because the gain changes relatively slowly, a compressor does not distort the signal in the way that a Limiter or clipping would do.

Parameters

• Threshold: Sounds below this threshold will be left unchanged. Sounds above this threshold will cause the compressor to reduce the level of the audio. It sets the vertical position of the corner on the graph (the yellow horizontal line).
• Ratio: The amount of compression applied to the audio once it passes threshold level. The higher the Ratio the more the loud parts of the audio will be turned down. The Ratio sets the slope of the graph above the corner (above the yellow horizontal line).
• Attack Time: How quickly the compressor reacts to an increase in volume, by reducing the gain. If volume changes are slow, you can push this to a high value. Short attack times will result in a fast responses to sudden, loud sounds, but will make the changes in volume much more obvious to listeners.
• Decay Time: How quickly the compressor recovers from a loud passage by increasing the gain back to the normal level. A long time here will tend to loose quiet sounds that come after loud ones, but will avoid the gain being raised during short quite sections like pauses in speech.
• Normalize after compressing: Boost the entire signal after compressing. Because the compressor works by making loud sections quieter, you will usually want to do this. If this option is selected, then the overall effect will be to make the quiet sections of the audio louder. One of the main uses of compression is to make it possible to amplify the signal, so the whole recording sounds louder.