So what exactly is a compressor? A compressor is a signal processor that is used to reduce the dynamic range between the softest and loudest parts of the audio signal. Think of the sound of your guitar as a wave. There is a peak where it is at its highest level and a trough where it is at its lowest. In the example below you will see signal wave with two lines running through it. The upper line represents the highest peak you can go to before your signal distorts or clips. This we will call the ceiling. The lower line represents the quieter or lower part of the signal that either is inaudible or gets drowned out by the rest of the band playing. This we will call the floor.
If you add a compressor to this signal it is going to close and lower the signal of the guitar if it starts to go above the ceiling and open and let more signal through when it starts dips below the floor. Now you won’t have clipping for the louder parts and the quieter parts will be heard in the mix. The signal would now look more like this.
Compression can be used on any single instrument or on the mix as a whole. Many bands and studios use compression on vocals because of the dynamic range of the human voice. Very high notes take more power to belt out and will sound louder that the low notes that sound softer because of the lack of power used to hit them. Using the compressor will make the singer have a more consistent range of volume. It also works great for live applications where the singer is constantly moving their head toward and away from the microphone. Bass players us compression to make a smoother sounding transition between notes.
Need more details on how to use a compressor?