Extensive compressor reviews and FAQ

 
Is it true that compressors are noisy? Can the noise be avoided?
 
All compressors, even the really expensive ones, have the potential to add noise. Most of them will add a bit of noise in normal applications. The reason is that compression reduces the peaks of your signal, which also brings down the average signal level. Our brains focus on the average levels, not the peaks, so reducing the peaks makes the whole signal seem quieter. To make up for that, nearly every compressor has a boost stage at the end, called "make up gain" (sometimes just labeled "level"). This gain stage boosts the level of the entire signal, including any noise that may have been in the signal path already from your pickups, preamp, pedals, room wiring, or a variety of other sources. You may not have noticed the noise before, but it was there- and the gain stage on the compressor just turned up the volume on it.
 
Additionally, any active signal processor may create a bit of its own noise, depending on how well it was designed and the quality of the parts used. So with compressors you get a combination of those two noise sources: noise that was already there in the signal, now amplified; and noise created by the actual circuit design and components of the compressor. That second noise source is where you can see improvement between a crummy cheap compressor and one of better quality. That's one factor in my reviews when I say a compressor has "low noise" or "more noise than I'd like". Good comps and bad ones will both amplify existing noise, but good ones are well-designed and made using high-quality components, and ideally should not add much noise of their own.
 
Now, to complicate matters a bit, there are many different types of compression circuit, and some types may be inherently more prone to amplifying noise. But it's hard to predict the results when shopping for a specific type of processor, as again it will vary depending on the way that particular model was built. Sometimes a comp may be designed to boost the high frequencies, which will result in more noise heard. Sometimes a pedal circuit will be sensitive to grounding issues anywhere else in the instrument-pedal-amp chain, resulting in hiss that's hard to solve. Some comps are designed with such low thresholds and high ratios that they can't help but boost noise a lot under normal use, even if the circuit itself is supposedly not noisy.
 
Another issue that I've run into many times is that some designs are very prone to picking up ambient electro-magnetic noise in the room. Tube compressors in particular give me endless problems this way. You may find that you have a tube compressor that I say is "too noisy", and you don't hear any noise at all. It's partly because you're in a different room, with different electro-magnetic fields.
 
However another factor is the system you use for listening to your sound. Some amps and speakers are not designed to reproduce the very high frequency range that noise occupies. Some bassists use cabs with no tweeters, or with the tweeter turned down. Some headphones have a limited frequency range. And some people tend to roll off the highs with an EQ. All of these options can contribute to not hearing any noise. Conversely, if you have a very high-fidelity listening system, or if you turn up the highs for a bright cutting sound, you will hear more noise than anybody.
 
Is there any way to combat the noise? Well, you can turn down the highs on your rig. You can eliminate other noise sources in your signal chain, such as overdrive pedals or any sort of extra amplification/gain/EQ/boost stages. You can check for ground loops in your rig- they can be hard to track down, but ground loops are a major source of noise that most people do not even realize is going on in their system. You can put any noisy items after the compressor instead of in front. As a last resort, you can use a noise suppressor or a noise gate- but honestly I would strongly recommend doing what you can to reduce the sources of noise before adding any gear that will alter your signal even more.
 
Very often, noise is caused by ground loops or other grounding (earthing) problems. There is no universal standard for the way circuits/devices are designed in terms of grounding, which means that some devices which work great on their own, or with certain other gear, will work terribly in connection to gear which was just designed a bit differently. Also since often the ground is internally connected to the metal housing of a pedal or rack device, any two processors may touch and connect through the metal rack and housings, resulting in a common ground- which may cause noise depending on the specific gear. Here is a very good article on the subject of ground loops: Rane Note.
 
Noise gates can be useful tools sometimes, but generally they are terrible at solving noise problems. There are exceptions here and there, but in my opinion 99% of the noise gates I've seen included in compressor units are worthless because they do much more harm than good to your signal. They chop your signal on and off, wrecking the natural attack and decay of your notes, while allowing all of the noise through for the duration of each note. In general, unless you are making intentionally choppy-sounding music, or recording/performing in a very dense mix, I would avoid using a noise gate. Even in the best of cases it will not eliminate hiss or hum from your signal path, it will only turn down the volume in between each note. Noise suppressors are an entirely different type of device. They operate by filtering the frequency range that noise occupies, and that can work well sometimes. But even then, I still think it's better in general to solve the source of noise problems, whenever possible, rather than trying to mask them.
 
Did somebody tell you that a compressor would help reduce noise in your rig? They were wrong! :)

 
 
All text on this page written and owned by Cyrus J. Heiduska, 2006-2010, all rights reserved.
Copying is prohibited, but please feel free to link to this page using the link text "compressor reviews".