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Get rid of that noise – The different uses for a Noise Suppressor

Do you suffer from uncontrollable feedback? Does your guitar pick up strange interferences at different venues, which your amplifier transforms into noise? Does the hiss from your gain pedals and/or from your amp’s preamp cause an infernal roar between songs? These problems are usually caused by lots of gain – meaning: fuzz, overdrive and distortion – in your signal chain.

A noise suppressor is a brilliant tool for any guitarist who thrives on more than just a little gain. Additionally, you can use it to create dramatic pauses in your songs, using the total absence of sound.


A noise suppressor (also called a noise gate) is a real problem solver, by being able to detect which part of the incoming signal is just noise and which is a guitar signal wanting to be amplified. A gate is a handy emergency device, when playing at different venues, each with its own set of electrical problems. A badly placed PA-system, electric generators nearby, or a cheap LED-screen can feed nasty interference and noise into your setup, making your show an uncomfortable onstage experience. A noise suppressor will help you avoid this.

If you’re aware of previous problems with noise you can include a noise gate at the planning stage already. A suppressor pedal is easy to integrate in a pedalboard.

ISP Decimator is the world’s leading noise gate

Back in the 1980s efforts to get rid of noise and hum were quite primitive. The devices on offer back then often had a negative effect on the whole system’s sound, and often caused an unnaturally chopped up signal. In those days the words “noise gate” seemed like a curse, but luckily times have changed. These days we don’t say “gate”, we use “suppressor”. State-of-the-art suppressors are designed to be “intelligent”, which means they can “read” the guitar signal and discern between musically sensible content and unwanted background noise.


An American called Buck Waller developed Rocktron’s first Hush Suppressor in the Nineties. It quickly became a must-have device, especially for guitarists in Metal bands. Later, Buck left Rocktron and set up his own company, ISP Technologies, where he went on to develop the industry standard for all noise gate pedals, the ISP Decimator. The updated Decimator II works even better than its predecessor. It is even more intelligent, resulting in very natural guitar tones. Special care has been given to detecting and processing held notes, which now fade away very naturally.

The standard version of the Decimator has been designed to be connected in series.

This circuit is also available as a mini-pedal called ISP Deci-Mate which takes up even less space on a crammed pedalboard. Both versions are completely identical in their electronic specifications, with both pedals offering the normal input and output jacks.

The ISP Decimator G-String includes two additional connectors – labelled “Decimator In” and “Decimator Out” – so you can put your noisy effect units in their own, dedicated noise suppressing loop.

The G-String runs two different tresholds to offer superior noise suppression. One circuit is dedicated to guitar signal detection, while the other is specialized in removing any noise. With this pedal, all gain stages in the signal path are put into the Decimator’s noise loop, before being sent on to any other effects and to the guitar amp. ISP’s labelling gives you a good idea of what goes where, as well as of the inner workings of the suppressor:

  • Guitar In – the guitar signal enters first enters the suppressor
  • Guitar Out – the guitar signal is sent on to the noise-inducing gain stages
  • Decimator In – the noisy signal is sent to the suppressor for cleaning
  • Decimator Out – the cleaned signal is sent to the next block in your effect chain on its way to the amp

How does noise enter my amplifier?

Before using any noise gate in your system, you should try to localize the source of the extraneous noise. If the hum and buzz is down to a faulty effect or amp, or if it is caused by an earth (ground) loop or a cheap power supply, the culprit is easy to spot: Plug in your guitar, turn on your rig, and then turn the guitar’s volume knob to zero.

If the noise remains unchanged the cause is someplace after the guitar in the signal chain. Theoretically, you could plug a suppressor into your amp’s FX loop as a quick fix, which would then do away with all noise coming from the front end of your signal chain, but this wouldn’t be how a suppressor is meant to be used. We would strongly recommend dealing with any and all noise-inducing problems in you signal path before using a suppressor, by using the easy test mentioned above.

Induced hum

If the extraneous noise only starts once the guitar’s volume is opened up, the noise is easy to remove with a gate.

We live in a world filled with electromagnetic fields, that induce 50 Hz hum (also called AC hum) into single-coil pickups. The easiest way to find out whether the hum you hear is induced, is to repeatedly open and close your guitar’s volume knob, while standing in different spots in the space you want to use your guitar in. It is also important to check that your guitar is properly shielded. Single-coils will always hum and buzz due to their design, you cannot change that, but a properly shielded guitar will suffer from much less noise interference, making it much less of a problem.

Induced electromagnetic interference is something you can’t hide from. Perfect protection could only be achieved by wrapping your amp and guitar – or even better: the whole room – in conductive foil, which is virtually impossible. as induced hum is the only thing completely out of our control, this type of noise is the one most people will use their ISP Decimator for. So:

  • If the problem remains after turning the guitar volume down, the noise is caused somewhere along the signal path of the rest of your rig. The instrument’s pickups reacting to any interference have been eliminated.
  • If the noise starts once you open your guitar volume potentiometer, it’s extraneous noise that is easy to fix with a suppressor.

The most common way of connecting an ISP Decimator

1. Connected to the guitar

Our starting point for using a gate is that all other sources of noise in the signal path have been eliminated beforehand. The power supply doesn’t buzz and the rig sounds clean. The last problem source should be the guitar’s pickups and the extraneous hum and buzz picked up from the environment.

If the induced noise is especially problematic, you can keep it at bay by plugging the guitar straight into the ISP Decimator, before the signal even reaches any other pedals. This is a efficient way of removing a venue’s generator-induced (or other) electromagnetic interference, which is usually worse with single-coils than with humbuckers.


If your noise problem is annoying acoustic feedback, plugging your guitar straight into the gate is the right solution, too. If the suppressor is set up correctly the sounds causing the feedback will be kept out of your rig, and kept from escalating into a problem further down the signal path. We don’t want to kill nice and musical feedback, though, because it is often a vital ingredient in a guitarist’s arsenal. If your rig is well put together, you will still be able to use musical feedback, despite using a suppressor. Often a suppressor even makes it easier to achieve musical feedback.

2. In series after gain pedals

Another situation where a gate will help you is if your rig is quiet with the guitar volume up, but the moment you step on a gain pedal – like fuzz or distortion – the hiss and background noise become unacceptable.

If your biggest problem is hiss produced by the diodes or transistors in high gain pedals, the standard version of ISP’s Decimator can be placed right behind the gain pedals, but in front of any delays and reverbs. Placed in this way the suppressor will leave any delay and reverb trails completely intact, while shutting up the noise coming from the gain pedals. In this way the effects following the gate will work much better, because they will be fed a clean signal.


3. Defeating gain pedal noise with an ISP G-String

 

Some fuzz pedals can produce too much noise for the standard Decimator model to function to full satisfaction. The pedal will cut the noise during pauses, but the threshold will have been set so high that some noise will be audible as a note dies away. We’d recommend using the Decimator G-String in these situations.

  • Guitar In: Plug the guitar into this jack directly. The Decimator will now be able to clearly detect each guitar note, before it is contaminated by noise.
  • Guitar Out: Hook up this output with the input of the first offending gain pedal.
  • Decimator In: The output of the last hissy gain pedal is fed into this input for noise suppression.
  • Decimator Out: The cleaned up signal is sent on to any following pedals, or directly to the amp.

4. Eliminating preamp hiss and gain pedal noise with an ISP G-String

Try to find out how much of the noise is produced by your amplifier. If the noise is present, even when you’ve plugged your guitar straight into the amp, and the guitar’s volume is turned all the way off, the hiss and/or hum is probably coming from your preamp valves (tubes). In many cases this noise can be a completely normal byproduct of your amp’s architecture, but you can “gate” this type of noise, too.


In this type of situation you would hook up the suppressor as one of the last devices in the amp’s effects loop, with serial loops working best. You can also use the gate between a rack preamp and a separate power amp. This will give you an extremely effective means of noise reduction in a high gain environment. Try to see if this setup works with your rig – the Custom Boards team has often gotten great results.

  • Guitar In: Plug the guitar into this jack directly. The Decimator will now be able to clearly detect each guitar note, before it is contaminated by noise.
  • Guitar Out: In this setup we think of the amp’s preamp as a noise-producing “effect”, too, which it often is. The signal first goes to all noisy gain pedals that are then connected straight to the amp’s input. If there are some other pedals you want to denoise, you can plug them between the gain pedals and the amp’s input.
  • Decimator In: In this example the suppressor is fed the signal off of the effect loop’s send (FX Send/Out). In this way all noisy pedals and the amp’s preamp section are chained through the Decimator for a clean-up.
  • Decimator Out: The cleaned up signal is sent to the effect loop’s return (FX Return/In). If you’re using a delay and/or reverb pedal, you should plug the Decimator’s output into the pedal’s input first, and connect the delay’s and/or reverb’s output to the FX Return, putting it right in front of the power amp section. Now the circuit is complete, and the ISP unit will suppress all noises produced by your pedals and the preamp effectively.

The noise gate as a percussive effect

A noise gate can do more than just remove unwanted noise. ISP’s Decimator can also be used as a pure effect, as many Metal guitarists have proven.

The use of a gate became de rigueur in some forms of Nineties Power Metal, which were based on fast and choppy riffs with many short rests. Many Metal guitarists still use this effect in their music. If you set the suppressor’s threshold very high, it will make the tails of the notes you play very tight and choppy, which will clean up your fast riffs by tidying the rests. This will add a lot of excitement and immediacy to your playing.

Remember that rests are a vital part of music; there’s hardly a more gripping means of expression than a full-tilt fuzz riff, followed by complete silence, which is then followed by another full-on power chord.

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