A true studio workhorse, the LA2A Compressor/Limiter
 

A compressor is a tool widely used in audio production.  Learning how to use a compressor in your productions gives them a more polished, professional sound.

Why Use a Compressor?

Audio has dynamic range. Dynamic range is the ratio of the loudest to softest levels in your audio. Compressors work to reduce that range by turning down the loud parts and turning up the low parts which make that sound upfront and more prominent in the mix. Properly compressing a vocal makes it stand out above the music playing under it. Compression can also add punch and character to a drum kit. There are many uses for compression in your productions. Lets cover the basics.

The Basics – Compression Parameters

	Threshold sets the point at which the compressor starts to work. A signal that goes above the threshold will be reduced. For example, if you set the threshold to -20db, any peaks that go above that will be compressed.
	Ratio is the amount at which a signal exceeding the threshold is turned down. You will see ratios of 1:1, 2:1, 3:1, 8:1 and so forth.  Ratios are measured in Decibels. Decibels are used to measure the loudness/Intensity of a sound. A ratio of 2:1 means for every 2db above the threshold, 1db is let out. 4db above the threshold would let out 2db. A ratio of 1:1 is called “Unity”… (no attenuation) 1db goes in and 1db goes out. So an input signal of 20db set with a 4:1 ratio would become 5db. Divide your signal level by the first number of the ratio to get your output.
	As the threshold sets the level at which the compressor starts to compress a signal, the attack time sets how fast or slow the signal is attenuated once it goes over the threshold. The unit of measure here is in milliseconds, MS. A smaller number represents a faster time. A fast attack time will act on transients immediately and a slow attack time will let those transients come through before getting compressed. A kick or snare drum strike for example, set with a fast attack time will be crushed, as opposed to a slow attack time that will let the initial strike come through before getting compressed, affecting the tail instead.
	As Attack affects the start time, the release time sets the time at which the compressor stops attenuating the signal once it falls under the threshold. Setting release times too fast cause an unnatural pumping in and out sound also referred to as “breathing”.  Set too low and the compressor never turns off.
	Some compressors have a “Knee” setting. The knee setting tells the compressor how hard or soft to apply the ratio setting. This is measured in db. You can tell the compressor to apply compression immediately or gradually to a signal once it has crossed the threshold , giving you more control over the overall compression.
	Applying compression actually reduces the overall level of a signal. To make up for this, you use the makeup gain parameter to turn it back up. When comparing the original signal to the compressed signal, use the makeup gain to match the original signals output to hear the actual effect being applied to the signal without being fooled into thinking the original, louder signal sounds better.

The famous 1176 Compressor/Limiter Black version