Apply a compressor to the individual instruments or components of your live setup to balance out the sound. Compressors can be used on instruments, such as a guitars or drum kits, to raise the volume of the quieter sounds that the instrument produces, while maintaining the level of the louder sounds. The softer sounds are amplified, while the louder sounds are compressed to prevent their amplification. The amplification of soft sounds and compression of louder signals, in effect, narrow the dynamic range of the complete mix.
Use a compressor as an effect on a component in your live sound. Adjusting the attack and decay can add interesting dynamics to your live sound. You can tweak the attack of your compressor to set how quickly the compressor reacts to sounds above the compressor's threshold settings. And you can adjust the compressor's decay to set how long the compression is applied to the signal after it reaches the compressor's threshold. Experiment with the attack and decay to find the setting that work best for you.
Use the compression technique known as sidechaining, or "ducking," to add emphasis to individual elements of your live setup. Sidechaining compresses the audio levels of a track on the fly. The compressor gives one audio signal priority over the other--when the primary signal gets louder, the secondary signal gets softer. Sidechaining is often used by DJs to automatically lower music levels while speaking into a microphone, sidechained into the audio feed.
Set up a limiter, a heavy amount of compression, to set a ceiling for the frequencies in your live sound. A limiter can be helpful to keep the frequencies of instruments from exceeding the available frequency bandwidth of PA speakers in your live set up. With a limiter in the mix, sound levels exceeding the set threshold of the limiter will be softened, or "clipped," and can prevent extremely loud sounds from blowing out your speakers.