The Boss Noise Suppressor NS-2 is a simple, but effective, noise gate that helps remove unwanted noise/buzz from your audio signal. The NS-2 is particularly useful if you are wanting to achieve a high gain tone without an earful of buzz every time you stop playing, very handy for quick, stop/start riffing. The NS-2 can also be beneficial for those using single coil equipped guitar and/or vintage pedals.
The Noise Suppressor NS-2 features three controls, Threshold, Decay and Mode. The threshold sets the threshold level for where the noise gate starts kicking it. This needs to be adjusted based on signal level and noise level. The decay controls the amount of time required to fade out when the input signal becomes lower that the set threshold level. Generally it would be recommended that you set this to minimum to start with, and if not satisfied, adjust to taste.
The mode control selects either the reduction or mute mode.
Besides the relatively straight forward controls, the NS-2 has a couple of other useful features that separate it from other noise gates on the market. Firstly it is able to bower up to eight other effects units, as the NS-2 can also act as a power supply. Secondly, it has Send and Return jacks so you can increase your looping and routing options. This is handy if you have one or two noisy effects that you would like to isolate from the rest of your signal.
The NS-2 is not supposed to colour the natural tone of your signal, however, there are mixed reports on how much coloration is actually noticeable. The NS-2 is used by a number of high profile guitarists, including Adam Dutkiewicz (Killswitch Engage), Jim Root (Slipknot), Tony Rombola (Godsmack), Wes Borland (Black Light Burns, formally Limp Bizkit) and Josh Rand (Stone Sour).
You can usually pick up an NS-2 used on ebay for around $40-$50, but it's worth checking out a few auctions.
