How to Mix Music – Using Compressors – The Basics
In the mixing stage of music production, there are a variety of hardware that we can use. These hardware generally fall into either processors or effects. A processor is a hardware that takes the complete signal and manipulates it entirely, completely changing the original signal. An effect however, only takes a part of a signal, applies effects to the signal, then returns the effected signal mixed in with the non-effected signal to produce an effected sound.
In general, a compressor is a processor to regulate the dynamics of a musical performance. It’s used to create a more consistent and clear sound. And as in any hardware, there are parameters we manipulate to shape and form the sound character that we want. The parameters of a compressor are:
1. Input Gain. This parameter functions to increase the signal coming into the compressor. Because compression is used to regulate dynamics, raising the input gain knob can increase the silent parts of the signal so we can hear it more clearly without raising the loud signals too loud because of the compression that happens. Which brings us to:
2. Threshold. The threshold is the value where the compressors starts kicking in. In digital music production, the loudest signal is 0 dBFS (decibel Full Scale). So for example, if we set the threshold at -24 dBFS, any signal that is louder than that will be compressed and any signal below that will maintain its original dynamics. How much compression happens is determined by the next parameter:
3. Ratio. The ratio determines how much compression happens by using a ratio such as 2:1, 4:1, and 8:1. What the numbers mean is this: for example, a 2:1 ratio means every 2 dB of signal that’s higher than the threshold will be decreased to only be as loud as 1 dB. The same for 4:1, every 4 dB of signal higher than the threshold will be decreased to 1 dB (a stronger compression ratio). Combining threshold and ratio, if the threshold is set at -24 dBFS and a signal peaks at -16 dBFS, with a ratio of 4:1 the signal will be compressed to peak at -22 dBFS instead.
4. Attack. Attack determines how fast the compressor reacts to a signal that crosses above the threshold. Attack is usually determined in milliseconds. For example, a fast attack setting would be around 5 ms: meaning, 5 ms after a signal crosses the threshold the compressor starts to compress the signal. An example of a long attack setting would be 100 ms. The fast and long attack settings determine the character of the transients (or the very early part of an audio signal): fast attack settings mean the transients get compressed also, while long attack settings mean the transient is allowed through while the body of the signal gets compressed. Transients are usually preserved for percussive instruments, such as the early “snap” of a snare.
5. Release. Release is the opposite of attack, and it determines how long the compressor maintains the gain reduction achieved after the signal returns to a level below the threshold. A short release means the gain reduction is let go immediately after the signal drops below the threshold while a long release means the gain reduction stays longer even though the signal is no longer above the threshold. For example, a longer release is usually used to maintain a sustained sound for the decay of a bass guitar.
6. Output Gain. The complement to input gain, output gain (or sometimes make up gain) is used to bring the audio signal back to it’s level in the mix after compression. Usually we want to use compression to even out the sound, but not make the sound smaller in the mix. That’s when we use the output gain to bring the level back to before compression.
Depending on the hardware or software plug-in that you use, the compressor might have more or less parameters than the four above (there are even compressors that are designed only with a single knob!). Such parameters might include high frequency or low frequency cut, a gain reduction meter, or others. Since each hardware of software has it’s own design and characters, the most important quality a sound engineer or mixing musician can have is the spirit of experiment! You never know until you hear it used in the mix.
Hopefully this article can help you to use compression better to make better mixes of your music.
To your compression excitement,