Today's Lesson

Compression is a useful tool that allows us to reduce the dynamic range of an audio signal making the loud parts quieter and the quiet parts louder. Compression is essential in taming musical elements that pop uncomfortably out of the mix.

There are 6 controls on a compressor:

• Threshold is the level at which compression starts to take place. If the signal does not breach the threshold it will remain unaffected. Any signal that breeches the threshold will be compressed. 
• Ratio determines how much compression occurs once the signal rises above the threshold. 

In a standard compressor, a ratio of 3 to 1 will output just one decibel for every three decibels that breaches the threshold. Similarly, with a ratio of 5 to 1, the compressor will output one decibel for every five decibels that passes the threshold.

• Attack time of a compressor is how long it takes to reach full compression. A steep downward slope is representative of a fast attack, whereas a slower, more gradual downward slope depicts slower attack times.

Slower attack times are great for when you want to maintain the transient detail of your sound, for example the initial snap of a snare drum, but bring down the overall level of louder sections.

A faster attack time is useful when we want to bring down the level of our audio peaks much more quickly and create a more noticeable effect.

• Release time as the opposite of the attack. This is how quickly the compressor will allow the signal to return to normal after compression has taken place.
• Knee affects how smoothly the compressor transitions between the point of attack and release. For a smoother and more musical handling of compression, you can set a soft knee where compression turns on gradually as signals approach the threshold and then passes it. Whereas a hard knee setting is going to produce a more noticeable difference in tone.

By design, a compressor will bring down the level of the peaks in your audio, which will result in the overall level being quieter at the output than the input. To remedy this, we use make up gain to bring the signal back up again after compression has taken place.

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