Short Description: Electronic device for placing all sound output levels within a set range. In short, nothing sounds too loud and nothing sounds too soft. This is a very important aspect in blending worship music. 

Details: Compression, or a compressor, can be described using very technical terms that are meanless to most people. I worked in the broadcasting field and we used a compressor called an optimod. It's the same idea. Play music from a tape or a CD. If you have a song that slowly fades away, you can hear it noticeably fade in volume. A compressor takes that dropping volume and boosts it up in volume. The result is when you listen to the radio and a song fades, you hear the song fade but the degree in which it fades away is much less. Likewise, crank up the volume of a home stereo and you could cause hearing damage. If a dj or sound engineer were to crank up the volume with a compressor in place, they will reach a point in which they are increasing the volume via controls but the output level does not increase. 

Compressors have the following terms/objects: 

• Threshold: When the compression will take affect. Measured in dB - isn't everything?
• Ratio: How much signal decrease for every 1 dB increase. Examples: Vocals (2:1) and Electric Guitar (6:1)
• Input/Output: Relates to the display lights and if you are seeing levels before or after compression.
• Hard Knee/Over Easy: Hard Knee is like a kick in the groin. It's an all at once type of feeling. Over easy has nothing to do with frying eggs but indicates a slow build up. Hard Knee tells the compressor to kick in once a threhold is reached. Over easy says "start compressing a little when I start to reach the threshold."
• Gain Reduction Meter: Shows the signal attenuation level.
• Attack: Determines how quickly compression will kick in. Generally short attack for speaking and long for percussive sounds.
• Release: Determines how long compression will occur after the signal drops below threshold. Short on percussion, longer on vocals.
• Output: Gain control for raising the signal after compression. Should be set to compensate for attenuation. Think of it this way, you want to compress but you want to maintain a certain output volume during compression.

Brands: DBX Audio, Rane