O no, not again, please… The questions on compressors and limiters and their definitions are just as old as the sound engineering field itself is. When you read explanations about compression and limiting, they all make perfect sense. However, the minute you put your ears to work, you quickly realize things aren't as simple as they sound. A great deal of expertise and skills is needed to become proficient in taming the two beasts.

Disc Makers blog gives it another shot at trying to explain what compressor and the limiter are. I'll let you be the judge of how well they did!

For many recording musicians, the compressor presents an enigma. Most of us know that compressors and their more specialized cousins, limiters, are used to control the dynamic range (aka volume) of an audio track or mix. But exactly how do they work, and from a practical point of view, how can you use them to the greatest advantage? We’ll provide a brief overview, and then head into the studio and see how the use of a compressor can help the recording process.

While dynamic changes in volume help give music its shape and emotion, too great a change in volume, and sudden changes, may create challenges when recording and mixing your music. Using a compressor or limiter allows you to smooth out passages where the volume may be too loud.

What’s the difference between a compressor and a limiter?
A limiter is a compressor, but a compressor is not necessarily a limiter. Limiters are designed to prevent the sound level of an audio program from going beyond a certain, pre set point. They generally have very high compression ratios of 20:1 variable up to Infinity: 1. (A compression ratio of 20:1 means that for every 20dB that the input signal increases beyond a preset point, the limiter will only allow output gain of 1 dB.) Limiters are critical for in-ear monitoring systems, radio and TV broadcasting as well as vinyl disc cutting systems. Limiters are seldom needed in a typical home recording session. Compressors will normally use lower compression ratios, often in the 2:1, 4:1, 8:1 range, meaning that the amount of gain reduction applied is not as drastic as with a limiter.

Compressors, on the other hand, are frequently used tools that reduce or control the dynamic range of a recorded track. A good way to envision the dynamic range of a track is the difference in volume between the loudest notes to the quietest notes. Compressors are handy for controlling many of the typical tracks you may be recording such as bass guitar, vocal, acoustic guitars, keyboard, etc.

Not every track will benefit from or needs to be compressed. If the original performance has a fairly limited range from the loudest to softest note, then compressing it will make little or no difference. However, if we consider a lead vocal track where the singer starts off near a whisper for the introduction and by the song’s end is wailing over a pounding band, putting a compressor on that lead vocal track may help reduce the dynamic range of such a vocal track so that it can easily stay on top of the band and allow for an easier overall mix.

Compressor Settings
The controls on most compressors are fairly similar. The first and most crucial setting is the Threshold. This is the point at which the device will begin to reduce the level of the output signal.

How much the signal is reduced is determined by the ratio. At a 2:1 setting, for every 2 dB of increase to the input signal beyond the threshold, the output signal level will increase by 1 dB. At a 4:1 setting, for every 4 dB of increase of input level beyond the threshold, the output level will increase only 1 dB. Higher ratios result in more dramatic gain reduction. If you have a home studio, put a compressor in your audio chain, and click between the different compression ratios available while you compress a track and you’ll quickly be able to discern which ratio works best on various instruments.

Two other controls affect the sound of the compressor. These are…

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