One of the many Electric Guitar Effects Pedals available to the guitarist is the Guitar Compressor. They come in many forms ranging from simple to complex, and can be used singularly or embedded within a multi-effects unit.

Firstly - what does Guitar pedals do?

Basically a Compressor automatically controls - or compresses - the Gain of the signal from the Guitar to reduce the Dynamic Range of the output audio signal to your Amplifier.

Note 1: Gain is a unit of measurement, which indicates the increase in power, or amplification of a signal through an Amplifier.

Note 2: Dynamic Range is (in this example) used to describe the ratio between the smallest and largest values of the audio signal.

The above sounds a bit Techy - so what are the practical uses?

1. In practical terms it means that with a Compressor, the player can perform a wide range of styles from soft chord work to loud lead solos, and the output - or volume -from the Amplifier would remain constant. This has the effect of enabling the audience to hear softer chord or rhythmic passages in the song while not drowning out the other musicians during your blistering solos.

2. Another popular use of the Compressor is to increase the sustain of a note beyond the natural string decay of the instrument. Gary Moore's Parisian Walkway is a typical example. The Compressor does not actually change the Guitars behaviour, but works on the audio signal to maintain a constant output level after the string has been plucked. In effect, by changing the Release Time to longer than the Guitar's Decay Time, the instruments note will be preserved.

3. One area where the Compressor is invaluable is in the Recording Studio. The Guitar is a very dynamic instrument, which can lead to all sorts of clipping and distortion problems for the recording engineer. The Compressor is probably the most used tool in the studio arsenal, and is used on most tracks to enrich the sounds - including vocals - as well as maintaining an even dynamic range to prevent clipping. In the modern day studio, which now uses computers to record music, the use of Compressors is now more often in the form of software plug-ins.

This has the advantage that the Compression settings can be changed at any time during the recording and Mastering sessions, and interacts and changes the sound of the audio signal without permanently altering the original recorded signal. However, with hardware Compressors, the signal is first passed through the Compressor before being recorded to the computer hard drive. Therefore, once the recording has been made, you cannot alter or undo the Compression effects.

This device has a number of uses for the live musician, but must be treated with caution as improper use can destroy the dynamics of the music, or lead to the introduction of unwanted noise. Generally there is no substitute for using your own ear to gain the experience to use a Compressor effectively, but the end result can be well worth the effort.