In my time with guitar/gear related forums, I have come across plenty of discussions about noise gates, noise reduction devices, etc. More often than not, only the devices are discussed and there are no discussions about the source of the noise or how to address it. Noise reduction/gating/filtering devices are not the be-all/end-all solutions to noise problems. Noise can be from a number of sources, anywhere from nearby electrical/RF/magnetic activity, insufficient shielding, improper or inadequate grounding, to just plain noisy devices. The noise should be addressed at the source. It can be a lengthy trial-an-error process but any noise reduction/gating/filtering devices should be the last thing you would implement, and only to address either any residual noise that the other solutions did not clean up, or in some cases, if everything else fails.
Examples causes and possible solutions:
Noise due to an improperly grounded amp:
Ground the amp properly.
Noise due to dying or microphonic tubes:
Get new tubes
Noise due to transformer (as in an adapter) with a big EMF in the vicinity of a sensitive device:
1. Move sensitive device away from the transformer;
2. use mu-metal to shield the transformer or the sensitive device;
3. get a transformer with a smaller EMF, like a toroidal transformer.
Noise due to ground-loop:
break the ground-loop (here is some info on ground-loops and how to address them:
http://www.rane.com/note110.html)
Noise due to a noisy guitar:
1. Shield the guitar;
2. Check the guitar's wiring, a star-grounding scheme might be in order
(check here for more info on shielding and star-grounding:
http://www.guitarnuts.com/wiring/index.php)
Noise due to a dirty/unfiltered power supply:
1. Get a better power supply;
2. Filter the power supply (this applies to AC power as well as DC).
Noise due to a microphonic p-up:
1. Re-pot the p-up;
2. Get new p-ups
Noise due to noisy effects circuit:
1. Have the effect modded to minimize, if not remove, the noise;
2. Get a better effects pedal
Noise due to excessive high-end content (hiss):
1. Bring down the treble/prescense, i.e. adjust the tone control settings;
2. Could be high-gain hiss: either turn down the gain or try cleaner sounding preamp tubes.
These are just a few examples off the top of my head. There are other causes/sources of noise and specific solutions to correct them. For instance, midi signal ground is isolated from the device's chassis ground. In my midi-controlled rig, one of the midi-plugs developed a short between the ground pin and the shell, causing a ground-loop. I had a tough time tracing this noise source. I ended up removing devices one at a time and checking all the plugs before I found the culprit.
There are also some situations where a noise gate of some sort seems to be the only choice. For example: I have a Mesa Boogie Triaxis preamp. I absolutely love the tones from this unit. However, some noise can be observed when in the high-gain presets. The guitars I use are already shielded and star-grounded, so that takes care of that possible noise source. Then there is the lone wah pedal that I run through, which is in a midi controlled signal switcher (looper). Whether or not the wah is in the chain, the noise is still there, so it is not the wah. If I plugged the guitar straight into the preamp and there is still noise. After the trial and error approach, I came to the conclusion that the noise coming into the preamp is exaggerated by the nature of the high-gain circuitry, nature of the beast so to speak. Could have been the p-ups being noisy but I like the p-ups and did not want to change them. I even tried using lower gain preamp tubes and/or cleaner sounding tubes. The results were either the noise was still present, or I did not like the tone. So in this situation, it seemed like the only logical solution was to use a noise gate.
The only question then was, where to place it in the chain. Before the wah? After the wah, before the preamp? After the preamp, before the power amp? There really is no one-and-only correct answer. It is up to you (or me in my case), where the gate will go, where it will give the best acceptable* result. Trying it before or after the wah seemed to have the same result, which was better than having it after the preamp. Having the gate after the preamp did not sound and feel natural to me. So, I just decided to have it as the first device after guitar and placed the gate before the wah. This give the preamp a cleaner signal to work with, there is a smaller noise level that the high-gain circuit can exaggerate. This was also gave me the most natural sound and feel (response). I also ran into this question when I was playing around with a pre-mod SD-1, and came to the same conlusion: place the gate before the noise generating device. After the mod, there was very little need for the gate.
*Acceptable results: Many times, a player gets too focused on getting a pristine, clinically clean sound. It might not always be attainable, in some cases you might have to sacrifice something to attain it. A player needs to determine what amount of noise is acceptable to him, and at what cost. Will the audience notice, or even care, if there is a minute amount of noise? Will the amount of noise be noticeable once the whole band is playing? Is the player willing to sacrifice the feel or vibe of his rig just to attain hospital-white cleanliness?
Anyway... Just some random, unsolicited thoughts about noise and noise reduction/gating/filtering solutions.
