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A compressor is nothing more than an automated level control that uses the input signal to determine the output level. In this video, I am going to show you all the parameters of a compressor and discuss how they each change the sound. All compressors have roughly the same parameter controls and are operated the same way, but they can sound different from one another because there are different ways of designing a compression circuit. Let's look at the controls. The first one is the Ratio control. Ratio controls how much of the output level the compressor will increase compared to level that's being fed through the input.
Usually this is calibrated in a ratio that goes anywhere from 1:1 to 100:1. And what that means is if it says 4:1, every 4 dB that's coming into the compressor, only 1 dB will go out through the output. The next control is the Threshold, and Threshold determines the signal level where the compression actually begins. Below the threshold point, no compression occurs, and above it is when all the compression occurs. Many compressors are calibrated in dB, so a setting of -5 means that when the level reaches -5 in the input meter, the compression begins to kick in.
Next controls are Attack and Release. Not all compressors have attack and release parameter controls, but most of them do. These controls determine how fast or how slow the compressor reacts at the beginning or the end of the signal envelope. The beginning is the attack and the end is the release. Some compressors have an auto mode that automatically sets the attack or release according to the dynamics of the signal. Some compressors have a fixed attack and release where you can't alter them at all. The Attack and Release controls are actually the key to proper compressor setup, but many engineers overlook these controls completely.
That being said, it's possible to get good results by keeping these controls set to midway, but learning how to use them provides much for consistent and professional results. Gain control is sometimes called makeup gain or output. When a compressor begins to compress, it actually attenuates the signal. So in order to boost the signal back up to where it was when we started, we use the Gain control, which adds some additional gain. Sometimes this is called makeup gain and sometimes it's just called an output control. We can use this additional gain for other things as well, and we'll talk about that in later movies.
The Gain Reduction Meter is an indicator of just how much compression is occurring in any given moment. On most devices, this is either a V or a peak meter, but it reads backwards. Let's take a look. (music playing) This means that if it reads -12, there is 12 dB of gain reduction actually occurring. If it reads -6, it means there is 6 dB of gain reduction occurring. It usually varies in the amount of gain reduction depending on the signal.
The sidechain is used for connecting other signal processors to the compressor. The connected processor only receives a signal when the compressor exceeds the threshold and begins to compress. Sidechains are often connected to EQs to make a de-esser, which will soften the sound of the S coming from a vocal when they exceed the compressor's threshold. You can also connect to delay or reverb or anything you want to the sidechain for unusual program-level-dependent effects. You can also feed the signal from another channel into the sidechain and will cause a sound to trigger from that original channel.
This is used a lot in electronic music especially. Finally, the Bypass control allows you to hear the signal without any gain reduction taking place. This is useful to help you hear how much the compressor is controlling or changing the sound. It also makes it easy to set output control so the compressed signal is about the same level as the uncompressed signal. So those are the parameter controls on a compressor.
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