Hands-On Review:ISP Technologies Decimatorâ„¢ Series

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The Decimator does noise reduction one better – it elevenates noise

By Darius Van Rheuhl
Musician’s Friend Staff Writer

There are two types of noise in the world: the kind we like and the kind we don’t. Noise from guitar amps fall into the latter category, and it does far more than just annoy. It can ruin a performance or recording with unwanted buzz or squeals, and its affects on guitar tone are far more insidious. Amplifiers, particularly high-gain amplifiers, add noise throughout the frequency spectrum that degrades tone. Plus, the combination of high gain levels and numerous effects pedals will cause uncontrollable feedback and squealing—the bane of recording and performing. Traditionally, expanders and gates have been used to control noise. But problems caused by the threshold and release controls found in these units include clipped attack transients, gate chatter due to "ripple effect" (fluctuation of level during long decays), and when it comes to feedback and squeals, well, let’s just say that both gates and expanders are out of their element.


So how do we eat noise, clipped attacks, feedback, and gate chatter, and have our high gain too? We don’t—Buck Waller, founder of ISP Technologies has done it for us with his Decimator Series of noise reduction units, that have become standard fixtures in the guitar rigs of Green Day, Aerosmith, Black Crowes, Anthrax, and guitar whizz, Johnny Hiland, to name a few.

It’s just a matter of time

If the name Buck Waller sounds familiar, it’s because he was also the founder of Rocktron and the inventor of Hush® noise reduction, for which he holds several patents. Today, Buck is still fighting the good fight with a unique approach to noise reduction in the form of Time Vector Processing (more patents for the Buckmeister), which solves the aforementioned attack and release problems.


The Time Vector Processing circuit continuously monitors the input signal and alters the release time with an incredibly fast, less than 1ms response and a 1000:1 release ratio (meaning it processes a tremendous range of signal variation). Whether you play a long sustained note or staccato, it senses the envelope and adjusts the release accordingly. The Decimator works with the guitar’s direct signal as opposed to sitting at the end of a long effects chain. The benefit of this approach is that instead of having only around a 10dB dynamic range to play with (which is what you get after amp and effects distortion), the Decimator is reading the 60-70dB dynamic range of the guitar. That gives it far more information as it tracks your playing, making it far more agile at reading input information while it prevents noise due to the microphonic characteristics of guitar pickups.

Duo Decimator system

The Decimator comes in two basic flavors: stompbox and rackmount. The controls of the Decimator G String pedal are quite simple: on/off and threshold. The pedal itself is sturdy enough to survive a limited nuclear attack.


And speaking of twos, the Decimator ProRackG is the world’s only two-channel noise-reduction unit designed specifically for high-gain guitar. One channel reduces noise picked up by the guitar, while the other, patched into the effects loop, eliminates amplifier gain noise. Along with the same downward expansion and TVP circuitry, it adds a dynamic filter, three ground lifters, and -10dBv/+4dBu operation. The Stereo Mod version handles dual amp setups.

Decimator ProRackG Noise Reduction System

Decimator Pro Rack G Stereo Noise Reduction System

Fizz is only good for gin

When recording heavy guitars, one of the hardest things for an engineer to do is to separate the fizz from the fuzz—that is, the high-frequency noise that adds dirt to your upper register. Generally, it’s done with EQ, which can kill tone on contact if applied improperly. And that’s where the dynamic low-pass filter of the ProRackG comes in. Also controlled by the TVP circuit, it tracks input frequency and adjusts bandwidth to allow the audio signal to pass unaltered. Any noise above the detected note frequency is eliminated.


As a high-gain guitar player, you’ve no doubt experienced uncontrollable bursts of feedback and squealing in-between staccato notes. By simply setting the threshold controls properly, the problem is solved forever. And, by using the input guitar signal to drive both channels’ level-detection circuitry, it eliminates the need to adjust the threshold setting every time you change gain or switch channels.

Yo, I ain’t no squealer

Does it work? Hell yeah! Using my Egnater Renegade and Tourmaster 412 angled stack, I plugged the amp and effects power strips into different untreated outlets to guarantee ground-loop noise; then I patched every analog pedal I had using wall-wart power supplies (noisy little buggers) into the effects loop; set the Renegade’s tube blender output to the brighter EL34s; cranked the gain, presence, and treble controls all the way; and kicked in the bright switches.


To set the ProRackG, all I had to do was start with the threshold controls fully counterclockwise, turn them up gradually, and instant Simon and Garfunkel—I’m talking sounds of silence. The amp seemed like it was on standby. Next, I turned up the dynamic filter until it cut the highs just a tad and then backed off on it a little bit. Here’s the amazing bit: The Decimator was completely transparent. After a lot of A/B critical listening, I heard no discernable difference in pick attack, and note decays were clean and natural during high-gain solos. Best of all, there wasn’t the usual noise floor ramping up to kill a note’s decay or reverb tail.

No noise is good noise

If you’re tired of noise messing with your Mesa, wondering why you can’t get the crunch you hear on records, or would like to eliminate hours of DAW editing, EQing, and futzing with noise-reduction plug-ins, the Decimator Series is the answer to your prayers. Once set, your high-gain, feedback-screaming amp will sound like it’s on standby—and when you play, all you’ll hear is pure tone, attack intact, and decays the way nature intended. It’s exceedingly rare that I plug something in, twiddle one knob and say $#@!—I have to get one of these!—especially if it doesn’t make a sound. But that’s exactly what I did say. Okay, I really didn’t say "dollar-sign pound-sign ampersand exclamation point" (it was something much more succinct and familiar). It’s also extremely rare for me to say this about any product: You won’t find a better noise-reduction system anywhere. What you will find when you put Decimator in your rig is your sound, clear and powerful, the way it should be.