Guide to Compression Types and Parameters

Introduction : If you are involved in audio, chances are you have run into compressors before. But you would be surprised at how often a do it yourself engineer doesn't understand the various functions in a compressor unit or plugin or the types of compressors that exist. Here's a guide that will set you on the right path. First, let's go over the various parameters.

Parameter One : Input - This controls the volume level your piece of audio is at before it reaches the compressor.

Parameter Two : Threshold - This signifies how high your volume signal must reach before the compressor activates.

Parameter Three: Ratio - This controls the strength of the compressor in accordance with the decibel rise above the threshold setting.

Parameter Four : Attack - This signifies how fast the compressor will work on the audio signal. A slow attack is a defining characteristic of optical compressors.

Parameter Five: Decay - This parameter will let you control how fast your signal returns to it's intended volume after being compressed. Again, a slow setting will give you an optical compression sound.

Parameter Six: Link - Certain compressors have this function. It will enable you have both your left and right channels work with compression.

Parameter Seven: Output - Controls the volume level of the audio after it has left the compression unit.

Next, let's go over the types of compression. Compression comes in many types, with certain types fitting certain applications better than other types of compression. Use your ear to experiment and choose the most appropriate type of compressor. I'll detail the ins and outs of the types of compressors available on the market.

Type One : Voltage Controlled Amplified Compression - Voltage Controlled Ampifier compression features an internal circuit that gives you extreme precision over the compressor. They are very transparent. However, they can also induce slight amounts distortion which can be both a good thing and a bad thing depending on the tone you're going for.

Type Two : Field Effect Compression - Field Effect Compressors utilize transistors and circuits to emulate a valve type sound without the valves. The clarity of these units are very prized, and their tone of often revered for it's natural precision. These are also another popular choice for vocal tracking. They are not limited to only that however, as these types of compressors can be heard on most any kind of instrument at one point or another.

Type Three : Optical Compression - My personal favorite. This type of compression centers on a light sensitive circuit that gently controls the amount of compression on a piece of audio. The attack on these units are naturally slower than other types of compressors, but the slow attack of these units are exactly what makes them so great sounding. This type of compression is ideal for vocals and is even used over entire mixes due to it's delicate nature. Often, these compressors have no threshold parameter because they are activated all the time.

Type Four : Valve Compression - Valves denote the internal parts of the compressor rather than the method of compression, but they sound so different they deserve to be their own type. Any of the aforementioned compression types can exist both with and without valves.

Final: Compression is one of the most incorrectly used tools for an engineer. When you realize what all the parameters do and what types of compression are available to you, you can finally use it correctly.