A compressor is a specialised amplifier used to reduce the dynamic range of audio (the range between the highest and lowest transients). Compression, broadly, is the act of reducing the dynamic range of signal. The entire signal can then me amplified during the makeup stage. Different types of circuitry are employed with differing results. Each of these results apply unique sonic characteristics suitable for individual applications.
To increase my abilities within the world of mixing it is important for me to fully understand the circumstances in which each type of compressor would be useful. Of course, this will develop in the applied use of different types of compression.
1. Tube Compression
Tube compression uses vacuum tubes to amplify a signal. The nature of the vacuum tube when driven results in a compression action with unique characteristics. Tube compressor’s tend to have a lower input response resulting in slow attack and release settings. This adds harmonic distortion to the sound which is often a desired qualities in mix engineers, in applications such as gluing. This process is nearly impossible to emulate across other types of compression.
2. Optical Compression
Optical compression uses a light emitting component in combination with an optical cell to attenuate the output signal. The higher the input signal, the brighter the light shines causing the attenuating circuitry to work harder. A famous example of this type of compressor is the LA-2A. The LA-2A also uses a tube element in the makeup gain process.
3. FET Compression
FET compression applies ‘Field Effect transistors’ in linear bistable operation, in place of Vacuum tubes, because they are cheaper to manufacture. These transistors by nature also react a lot quicker than vacuum tubes and therefore provide a more punchy compression sound. This makes FET compressors good for applications such as parallel drum compression. An example of a FET compressor is the 1176.
4. VCA Compression
VCA or ‘Voltage Controlled Amplifiers’ compressor employ solid state or integrated circuits to compress a signal. VCA compressors tend to be cheaper than the other varieties or compressor. They also provide much less colouration. An established example of this compressor is the DBX160.