# Hush/Noise suppression pedals in the amp's effects loop?



## studiodog (Sep 10, 2010)

Hi folks,

I recently acquired a Roland JC-90 amp (Sweet! I've wanted one for years!). Mine has the typical JC hiss in the preamp section - in a live situation or noisy bar it's not noticeable but for quiet practice it's annoying. So I'm looking for a way to tame the hiss, which I understand from other owners is just the way the JC amps are. It's a design flaw that Roland hasn't bothered fixing. Weird, but whatever....

Anyway, I've been looking online at various noise reduction pedals and thought I'd seek opinions here. I'm specifically looking for a unit I can insert in the amp's effects loop. My research so far indicates that units like the Rocktron Hush and ISP Decimator might work for this application. Anyone used these? Are there others I should investigate?


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## david henman (Feb 3, 2006)

...the ebtech hum eliminator is affordable and may be what you need. it even helps to quell single coil hum.


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## studiodog (Sep 10, 2010)

Hi David. Thanks for the post. Just to clarify, I'm not dealing with ground hum in this instance (although I get it when I run to two amps). The issue with the JC90 noise is that the preamp section is hissy. IE when I plug a guitar into the amp, there is a noticeable hissy noise floor; however, if I run my Boss ME-25 multifx into the stereo effect returns on the JC, there is no hiss. What I'm looking for is a noise reduction/suppression system to use in the amp's effect loop to quell the preamp's innate hiss. 

The EBTech is meant to remove ground hum from noisy guitar pickups, ground loops etc, so it not applicable here. As I said, I do get ground hum issues when running two amps, and that's where the EBtech comes into play.


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## david henman (Feb 3, 2006)

...you may be right, although the ebtech is deisgned to be used in the fx loop. 

a noise supressor like the isp decimator may be the tool for the job, as long as it doesn't mess with your tone or dynamics.


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## mhammer (Nov 30, 2007)

About a dozen years ago, there was a magazine called "Performer's Audio". You can read about its pedigree here: Performer's Audio; New magazine for musicians, audio & studio technicians | Business Wire | Find Articles at BNET It last for maybe 2 years, then tanked. 

In one of the early issues, there was an article about using the PAiA Hiss-Whacker ( PaiaTalk - View topic - 9304 HissWhacker ) as an add-on insert in an amp in pretty much exactly the fashion you are contemplating. The HW was a downward expander. The Hush unit (and SSM made the HUSH chip for a while SSM2000 datasheet pdf datenblatt - Analog Devices - HUSH Stereo Noise Reduction System with Adaptive Threshold ::: ALLDATASHEET ::: ) is also a downward expander.

I have the issue and can scan the article for you if you wish, though it should be noted that SSM no longer makes the requisite chip so you can't exactly buy a Hiss-Whacker kit and follow up. The basic principle of inserting some downward expansion into your signal path is sound, however. The caveat is that any device that functions by detecting the level of something, and then adjusting accordingly, makes some assumptions about what the range of levels to distinguish between will likely be. If the critical range of levels is compatible with what is present at that patch point, groovy. If not, then some sort of adaptation may be required.

I made myself a compressor using SSM's 2166 chip, which also has on-board downward expansion capabilities, and that sucker is as quiet as death, without any apparent imposition on audio quality, note attack/decay, or any of that. Highly recommended.


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## studiodog (Sep 10, 2010)

Hi guys. mhammer- I'd be interested in reading that article if you don't mind sending it out. The downward expansion idea is, as I understand it, the theory behind pedals like the Decimator, which is kind of a mix of noise gate and expander. I can't find one locally, so I can't test it in my rig, but I'll keep my eyes open and try to demo it at some point. 

I have been busy today (my day off), trying various combinations and permutations of gear to see what results I can achieve. I borrowed a BOSS NS-2 noise suppressor from my local shop to try out, but I don't like the sound - it acts purely as a noise gate, so while the hiss is gone when I'm not playing, it comes back in full force as soon as I touch a string, which is not what I'm aiming for, so I'll be returning that unit. 

Going on the EBTech hum killer theory, I jacked in the cheap-ass Behringer HD400 Hum Destroyer I had picked up a few weeks ago to remove the ground loop hum from my multi-amp setup, and it does indeed remove quite a bit of the background hiss! Thanks to David for that hint! And surprisingly, there is little to no obvious degradation in tone! 

The HD400, however, also attenuates the output volume significantly if inserted in the fx loop on its own. I found, purely by chance, however that if I insert an EQ pedal or other buffer in between the HD400 and the FX return on the amp, I get the volume back! Not sure why (impedance matching, I suppose), but at this point, I'm not knocking it! I ended up running the output of the HD400 through a BOSS FV50L volume pedal I had planned to sell. I used all TRS balanced cables from the FX send on the amp, through the HD400, FV50L and back to the amp's fx return. Not only is the amp a lot quieter (hiss is attenuated by about 70%), but I also now have a volume pedal to control the amp's final output level. Nice! Even nicer is the fact that it hasn't cost me a cent extra, as I had all the bits lying around the music room! (BIG points on the Spousal Approval Meter - Yay!)

I'm going to track down a 3-button footswitch to control the JC's distortion/reverb/chorus channels, and that should set me up for the electric side of my sound. Those of you who have followed my other posts know that my guitar is set up with a piezo bridge for acoustic tones. With the money saved here by recycling old gear, I've got a bit more leeway to order that Radial Tonebone PZ-Pre DI/Preamp system that will let me share one mixer channel between the piezo output of my guitar and my mandolin!


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## studiodog (Sep 10, 2010)

For the graphically inclined:








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## mhammer (Nov 30, 2007)

Yep, the HD400 is likely to play havoc with impedance matching in a number of contexts like yours, particularly given that amp FX loops are designed to anticipate devices with potentially higher input and output impedances. 

Generally, gates and expanders are not used in tandem, simply because the one interferes with the functioning of the other, and the other makes the one redundant. Downward expansion works in a diametrically opposite way to limiting. Where a limiter translates increases in signal above a certain threshold to *smaller* proportional increases (which is why they have controls legended with things like 2:1 4:1 etc., implying that the increase in output will only be 1/2 or 1/4 that of the increase in input), a downward expander exaggerates changes in volume below a certain threshold such that small drops in input signal level are translated into larger drop in signal output. One is "Gimme a dime and I'll give you a loonie" and the other is "Gimme a loonie, and I'll give you back a dime".

Many level-dependent niose-reduction devices rely on the principle of "masking". That is, noise will not be noticeable when there is an abundance of signal to occupy the attention of the listener. As the signal level declines, noise becomes more noticable and thus more objectionable. Noise filters operate like an auto-wah to remove top end (where the hiss lives) as the signal level declines. Many authorities feel that a bit of downward expansion and some noise filtering provide a very nice unobtrusive form of noise reduction.


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## studiodog (Sep 10, 2010)

Here's a link to the ISP Decimator White Paper. 

Decimator White Paper

Seems it's a souped-up downward expander with a few extras....


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## mhammer (Nov 30, 2007)

Thanks for that. Interesting read.

And yes, a souped up downward expander. That's not a BAD thing, just not a miracle.

I still maintain that if a circuit is taking action based on level-detection, the best place for it to detect that level is the point at which the dynamics are the least constrained. Now, while it is clear that the effects loop provides a great insertion point for a last-gasp intervention, there is a pretty good chance you'll be constraining the signal dynamics in some fashion before it gets to that insertion point. That could be a matter of using a compressor or overdrive ahead of the amp, or using the amp's on-board overdrive (which will be in the front end). That is necessarily going to make it harder for you to set the expansion threshold in a way that both successfully addresses the noise and doesn't audibly interfere with the nuances of signal.

The ideal is to have the _level-detection_ take place as early as possible after the guitar output jack, but apply the downward expansion itself at the FX loop insertion point.

I fully realize that may be very difficult to do in many instances. I'm just saying what the "ideal" is.


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## studiodog (Sep 10, 2010)

mhammer said:


> The ideal is to have the _level-detection_ take place as early as possible after the guitar output jack, but apply the downward expansion itself at the FX loop insertion point.


I think this is the theory behind having the guitar plugged directly into the Decimator G String pedal. I don't know anything here for sure, but it would seem that the level detection could happen at the input jack and the downward expansion as part of the send/receive loop? I have to admit getting easily confused ready tech papers - I'm no engineer, just some shmuck trying to make music.:rockon2:

Really wishing I could get my hands on a unit to test! It's pricey, at $220 or so at Long & McQuade, but if it actually works as advertised, I would be sorely tempted!


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