The MXR 102 Dyna Comp is a compressor effect guitar pedal, released in 1972 by MXR and rapidly becoming popular because of its price and ease of use. The electronic circuit was also used as a reference design on many other compressor effects like the Ross Compressor, T-Rex CompNova, Ibanez/Maxon CP5/CP9/CP10 and boutique pedals. This model is neither the most silent nor the most hi-definition piece of gear but it has real character and it's easy to find.
This pedal produces dynamic range compression, this is basically smooth out volume differences between notes; giving more body and level to weak notes so the sound does not change drastically no matter what the real signal level is, giving better articulation and sustain to the guitar. The pedal also adds its own coloring and tone to the signal.