Invalid Link Removed <--- Page 44: Compression Basics. It's easier to understand compressors when you can visually see what it does. Even better is to play with a graphical compressor, gate, limiter, etc. Not all compressors are created equal. You have slope, soft and hard limiting circuits too, depending on how it was implemented. The MXR M87 does soft limiting at 12db and hard limiting at a 20db ratio setting, for instance, and even brickwall if you set the attack to as fast as it can be. The nice thing about the MXR is that you can visually see the compression based on the input gain and understand the effect of lighting it up solid the whole time -- which just means that the compressor output is reducing the volume a certain amount based on the input sensitivity and doesn't hurt the compressor. A compressor used as a limiter can be used to protect speakers from sudden spikes that could damage them.
That said, you can still blow your speakers even with a compressor in place if your amp is rated higher than the load the speaker can handle. Another case is where your compressor's attack is too slow to react to a sudden full spectrum spike (eg. stepping on a cheap instrument cable and yanking it out of your guitar on stage in the middle of some loud playing). If the initial transient gets past the attack setting, the result is that it will hit your speaker and could blow it (given high or excessive volume).
In mixing and mastering, it's common to run a compressor and a limiter in the same signal chain. Limiters aren't always used for spike protection (you can just turn the volume down for that), they are also used to raise the volume floor of really soft sounds.
Even with all this knowledge, reading, etc. compressors are still a magical, difficult to master part of the signal chain, can really change your sound and playing for better or worse and can help you achieve different goals depending on where they are in the chain and how you want to use it. I have an M87 just after my envelope filter on the pedal board, I find it helps get a certain sound. I also have a built-in compressor on my Mesa M9 Carbine, which I keep around 9 o'clock on threshhold and ratio for a really subtle compression effect.
