Large studios use multiple compressors, and some mixing boards have compressors built into each input channel. A compressor basically works like an automatic level control, restricting the overall dynamic range of an input signal. In other words, it limits the amount of variation between the loudest and the softest sounds. Proper use of a compressor can prevent distortion from overload during loud sections of a song, smooth out unintentional peaks and drops in a performance, and provide additional sustain for electric guitars. Improper use can add unwanted noise or accentuate noise already present in a signal.
Excessive use can destroy the dynamics of a piece.
With that in mind, let's take a look at how compressors work, and how they can be used to enhance your recordings. The most important control is the threshold control. It tells the compressor the level that the signal must be at in order to start working, and it's expressed in decibels, abbreviated dBs . If your guitar signal comes in at -31dB, nothing happens. If the signal is -29dB or higher the compressor starts to work by reducing the gain of the signal.