The ISP Technologies HUM EXTRACTOR + DECIMATOR G RACK is a two-channel rack-mount noise reduction system that combines two separate jobs in one box. The Hum Extractor half removes power line frequency hum, the droning 60-cycle tone that comes from stray magnetic fields generated by transformers or power lines near instrument pickups. The Decimator G half is a noise gate that ISP Technologies rates at a maximum of 80dB of noise reduction1.
The two sections address different problems. Hum is a fixed, low-frequency tone that a gate struggles to remove cleanly, because it sits inside the guitar's low end. By extracting the hum first, the unit lets the Decimator circuit work on the remaining broadband hiss and noise. ISP Technologies describes the whole design as patent pending1.
A pedal version of the same circuit exists as the ISP Technologies Hum Extractor + Decimator G; the rack unit carries the same specifications in a single-space rack chassis12.
Hum removal and noise reduction on two channels
ISP Technologies positions the unit as a "two channel, ultimate noise reduction system"1. The Hum Extractor addresses the specific problem of power line hum, which the maker says is most commonly caused by stray magnetic fields from transformers or power lines near instrument pickups1. This is the noise a player hears change as they rotate or move their guitar around a room, and it is a different problem from the hiss and broadband noise produced by high-gain pedals and amplifiers, which is what the Decimator side handles.
The Decimator G circuit in this rack is part of the same family as ISP's standalone noise reduction pedals, including the ISP Technologies Decimator II and the ISP Technologies Deci-Mate. RockBoard's PedalPedia classifies the unit as a noise gate3.
The unit runs on 9VAC RMS at 1.5 amps1. This is an AC supply, not the 9V DC center negative power used by most pedals, so it needs its own supply rather than a pedalboard power brick or daisy chain.
Levels, noise floor and frequency response
The rack unit's audio specifications, from ISP Technologies, are as follows1:
| Specification | Value |
|---|---|
| Maximum input signal | +13.5dBu |
| Input level trim | 21.5dB, input level -8dBu to +13.5dBu |
| Output max level | +13.5dBu |
| Noise floor | -104dBu A-weighted |
| Dynamic range | 117dB A-weighted |
| Frequency response | 20Hz to 20KHz, +0 / -.5db |
The input level trim of 21.5dB, covering an input range of -8dBu to +13.5dBu, lets the unit match sources at either instrument or line level1. The frequency response of 20Hz to 20KHz within +0 / -.5db means the unit passes the full audible band without coloring the tone, and the -104dBu A-weighted noise floor and 117dB A-weighted dynamic range indicate the circuitry itself adds very little noise while removing it1.
The maker gives these level figures in dBu throughout, with the noise floor and dynamic range both specified as A-weighted1.
Power and size
The unit is built for a single rack space: 7.15 inches wide, 1.85 inches high and 4.5 inches deep, weighing 1.2 pounds1. Its 9VAC RMS / 1.5 amp power requirement sets it apart from most modern noise gates, which run on 9V DC and sit on a pedalboard. Players comparing rack noise reduction options can also look at the Rocktron HUSH Super C and Rocktron HUSH Ultra, or at pedalboard alternatives such as the Boss NS-2 Noise Suppressor and TC Electronic Sentry.
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Questions
What does the Hum Extractor part of this unit do?
The Hum Extractor section removes power line frequency hum, the low-frequency noise most commonly caused by stray magnetic fields generated by transformers or power lines near instrument pickups. ISP Technologies describes the design as patent pending, and it works ahead of the Decimator noise reduction so the gate only has to deal with broadband hiss rather than hum.
How much noise reduction does the Decimator section give?
The Decimator section provides a maximum of 80dB of noise reduction, according to ISP Technologies' specifications for the rack unit. That figure applies to the Decimator channel of the two-channel system.
What kind of power does the Hum Extractor + Decimator G Rack use?
The rack unit runs on 9VAC RMS at 1.5 amps. This is an AC supply rather than the 9V DC center negative power most guitar pedals use, so it cannot share a standard pedalboard power supply.
Is the Hum Extractor + Decimator G Rack one rack space?
Yes. The unit measures 7.15 inches wide by 1.85 inches high by 4.5 inches deep and weighs 1.2 pounds, which fits a single rack space.
What is the input impedance?
The input impedance is 470K ohms, as listed in ISP Technologies' specifications. That is in the same range as a typical guitar amplifier input, so it preserves the high-frequency content of passive pickups.
Is the Hum Extractor + Decimator G patent pending?
Yes. ISP Technologies describes the Hum Extractor + Decimator G as patent pending on its product pages for both the pedal and rack versions of the unit.
Sources (3)
- ISP Technologies, ISP Technologies
- ISP Technologies, ISP Technologies
- Hum Extractor + Decimator G by ISP Technologies, RockBoard PedalPedia, 2026
