In Part 1 we talked about reverb, delay, chorus, and flange. These are the “echo” or “delay” effects. In Part 2 we will discuss what compressors, limiters, expanders, and gates do and how they can be used. Note that these effects are what we call “control” or “behind the scenes” effects in that they do not intentionally modify the sound for variety or the enjoyment of the listener … rather, they control the basic sound so that it behaves itself. Let’s see what we mean by this …
Compressors:
What does a compressor do? Compression is arguably the effect most misused by guitarists. This misuse is probably because many players do not understand what compression is or what it does. When a new guitar player gets hold of a new effects unit they expect that it is going to alter the sound of the guitar in a very noticeable way. A compressor is not this kind of effect. Think of it as a ghost in the shadow of the effects chain. If you weren’t looking very hard for it you would not even notice that it was there.
So what exactly is a compressor? A compressor is a signal processor that is used to reduce the dynamic range between the softest and loudest parts of the audio signal. Think of the sound of your guitar as a wave. There is a peak where it is at its highest level and a trough where it is at its lowest. Sometimes these highs and lows get out of hand; that is, the highest levels start clipping, and the lowest levels are drowned out and are inaudible in the mix. A compressor reduces the highes and brings up the lows so that your dynamic range is, well … compressed. This stops the clipping of the louder passages and improves the sound while preventing costly damage to your equipment. It also brings out your quieter passages so that the listener can hear them.
Compression can be used on any single instrument or on the mix as a whole. Many bands and studios use compression on vocals because of the dynamic range of the human voice. Very high notes take more power to belt out and will sound louder than the low notes that sound softer because of the lack of power used to hit them. Using the compressor will make the singer have a more consistent range of volume. It also works great for live applications where the singer is constantly moving his head toward and away from the microphone. Bass players use compression to make a smoother-sounding transition between notes.
One of the benefits of compression on a guitar is the longer sustain of notes or chords. As the signal is starting to dip below the floor, the compressor will open up and let more signal through. This will allow the signal to be audible longer resulting in more sustain.
You will need to set up four main parameters on a compressor. These parameters are the compression ratio, threshold level, attack time, and the release time. The compression ratio sets the level of compression that will take place once the signal reaches the threshold. A 3:1 compression ratio would mean that for every 3dB of signal above the threshold there would only be a 1dB increase at the output. The threshold level is the level the signal needs to reach in order for the compressor to kick in and start working. The attack time is the amount of time it will take the compressor to react to the incoming signal. The release time is the amount of time it takes for the compressor to allow the signal to return to a normal level.
There are two main types of compression—hard knee and soft knee. The knee is the moment that the compressor starts to reduce the gain when the signal reaches the threshold. Hard-knee compression cuts the signal off abruptly when it reaches the threshold point. Soft knee is a smoother gain reduction that lets the sound taper off at the threshold point. Most good compressors on the market today let you switch between hard knee and soft knee.
It is very important to understand that compression can be overused and cause your signal to sound flat and weak. Use it with care, experiement with it, and improve your sound. Remember, a compressor is a tool to tweak your sound – use it carefully. Just as seasoning adds to the flavor of a good dish but too much can ruin an entree, so goes compression.
Limiters:
Limiters are quite similar to compressors. As we talked about earlier, a compressor reduces louder signals of your instrument. Unlike a compressor, a limiter completely cuts the signal off at the threshold. It is a great device to save your sound system from hitting levels that can damage or destroy it. It will not let your signal go above the maximum level you set. So unlike a compressor, the limiter is only going to deal with the louder levels of your signal.
Expanders:
Expanders are completely the opposite of compressors. Whereas a compressor is going to reduce your signal into a set parameter, the expander is going to widen that signal within set parameters. Why would you want to do that? An example of the use of an expander would be finger-sliding sounds on an acoustic guitar. Let’s say that you have the finger-sliding sound coming through your mix on the lower end of the audible signal. If you expand or exaggerate the signal dynamic width, it will push this sound further down into the mix so it will not be so pronounced. Another example would be breathing sounds from a singer at the microphone. Again if the signal is expanded it pushes unwanted sounds further down the audible signal. An expander is usually used to reduce unwanted background noise in the mix.
Gates:
A gate works like a limiter but at the other end of the signals dynamic range. A gate cuts the signal off below the set parameters level. Unlike the compressor which pulls the lower level sounds up, a gate chops it off completely. Like an expander it is used to keep unwanted background noise out of the mix. One very common use of gates is miked drums. When the drums are miked up individually, you do not want other drums sounds bleeding into the wrong microphones. The gates cut off the signals bleeding over from other drums and clean up the mix. This is effective in keeping the cymbal sounds from bleeding over onto the tom tracks. It is used most dynamically on the snare drum mic and hi-hat mic because of their close proximity. Gates work well with guitar for eliminating the hiss and unwanted noise heard when the instrument is not being played.
So where should these effects be put in the effects chain?
There are two schools of thought on where to put compression in the effects chain. The first is that it should be at the beginning, so a smooth clean signal hits all of the other effects. I do not buy into this method personally because I know that some effects are going to cause the signal to clip again. The method I like is to put it after all the effects except the echo effects like reverb, delay, chorus, and flange. I want to compress all the effects in the signal but let the reverb-type effects fade out naturally. Both methods work for different people so you will want to try them both and see which works best for you. These methods also apply to limiters and enhancers. As far as a noise gate goes, I like them at the end of the effect chain so they cancel out any residual noise caused by the effects unit, especially flange. Flange has a tendency to cause a lot of background noise when the guitar is not being played.
Next time, we’ll look at Overdrive, Gain and Distortion. Aren’t these all different names for the same effect? Actually, no. They’re similar, but not the same thing. Stay tuned! Until next time, I’m Frank the Tech Guy.
