This one isn't actually strictly an "effects" pedal but it is a *really* useful piece of kit for reducing the latent noise in your rig. So all those noisy but great sounding vintage FX pedals no longer have to add all that hiss. It'll also cut out all the 50Hz hum from your single coil pickups too. It's not a typical "noise gate" with the classic issues around tone sucking and note cut off.
Here's the description from the ISP Website;
"ISP Technologies presents the latest generation in high performance Noise Reduction technology, the DECIMATOR™ NOISE REDUCTION SYSTEM.
From the original inventors of the HUSH® noise reduction comes the latest, most advanced, patent pending, state of the art technology in real time noise reduction. The Decimator offers a revolutionary breakthrough in Noise Reduction processing with an unparalleled level of performance. The HUSH system, as well as all other noise reduction systems suffers from one major problem inherent in their design: The system cannot be immediately responsive to both very short-term staccato notes and long slowly decaying signals. The typical downward expander noise reduction system suffers from a dead zone in the release response characteristic, which causes a compromise in tracking both fast decaying notes and long sustained notes.
The Decimator design offers a novel approach to tracking the envelope of the input signal called Time Vector Processing. Due to this novel approach in controlling the expander, the Decimator system will instantly respond to short staccato notes and, at the same time, will provide a very slow ripple free control of long sustained notes. This means that the Decimator noise reduction system is the most transparent and highest performance noise reduction system available. The Decimator Pro Rack uses both Dynamic filtering and low-level downward expansion. A Time Vector Processing circuit controls the release response of both the downward expander and dynamic filter."
Here's a demo video of the ISP Decimator from Tone Factor;
Here's the Decimator white paper from the ISP website, there's some useful information in here;
Thanks to some great work reversing an original on DIYStompboxes.com (original thread here; http://www.diystompboxes.com/smfforum/index.php?topic=88902.0) there's a schematic and a PCB layout available from Joao Galego;
For those of you who like to work with vero here's a verified layout from Harald Sabro; http://www.sabrotone.com/?attachment_id=1380
There's also the Decimator "G-String" (Interesting name!);
"The Decimator G String provides a totally independent channel of Decimator noise reduction that can be inserted into a series effects loop or after a preamp section with the advantage of having the Decimator level detectors track the guitar signal directly. With the G String pedal you can set the threshold and no matter what level of noise the Decimator will track perfectly without any side effects.
The amazing thing is that you can switch from high gain to your clean channel and never have to switch the Decimator G String off due to the threshold being set too high. It’s simply transparent.
As can be seen in the diagram, the G String noise reduction pedal has an input to connect a guitar directly and a buffered output signal to feed the front of a guitar rig directly while providing a separate audio channel of Decimator that can be inserted in the signal chain of any guitar rig. You can insert any other pedals between the output of the Decimator G String and the input of your guitar amplifier. This allows the Decimator G String pedal to remove any level of noise you may have even with overdrive pedals at the front end of the amp."
Here's a work-a-like designed by Galego, notice the clever use of the buffer and FX loop to allow the G-String to do it's thing;