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How do the Compression pedals work?

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Which compression pedals do you use? Which provide the best effects? And how do they really work? I'm trying to get a better understanding of the various setting options.

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I had to explain this to our bass guy a few months back and you are asking about IMO one of the most useful effects.


This thread is pretty good and saves me typing :)




Here is a snippet:


A common story to explain a compressor is something like:


There's this little gremlin.


His job is to listen to the music and turn down the volume when it gets too loud.


The "Threshold" is how loud the volume has to be before a red light comes on and the Gremlin grabs the volume fader and brings it down.


The "Ratio" is how much the Gremlin brings it down. The ratio is "how many decibels out:how many decibels in". So, a 1:1 ratio means that for every 1 db that comes in, the compressor lets 1 db out. A ratio of 4:1 means that for every 4 db that comes in, 1 db is let out. A ratio of 20:1 is the same, but this is considered a limiter.


The "Attack" is how long it takes the Gremlin to see the red light, get off his chair, grab the slider and pull it down. Long attack times let the transient or peak of the audio through before lowering the volume. This can accent the "punch" of a sound by making the transient even bigger compared to the rest of the signal. A shorter attack time will eventually cut off the transient too-which is what a limiter would need to do.


The "Release" is how long the Gremlin keeps the fader down after the audio gets quieter than the threshold, and the red light goes off. If the release is short, then the sound will pump more-meaning that the sound will get quieter on a peak and immediately louder again after the peak is over. A long release time means that some of the notes after will be lowered in volume still, even though they are below the threshold.


Compressors often have a "gain" knob at the end. Keep in mind that Compression ONLY make things quieter. The gain knob is there to bring the sound back up in volume after you squished some of the peaks. Since you altered the peaks to make them quieter, the average level of the peaks is closer to the level of the quieter parts. Mountains are now hills. Turning up the gain makes the whole track louder overall. This makes the "sustain". The quiet parts that faded out are now louder and it makes the note seem like it lasts longer.


That about sums up how they work. The differences in settings and types of compressors can have a big difference on the sound. For example, an Opto compressor (it literally uses a light bulb to trigger the compression) is slower than say a digital compressor to attack and release. This makes vocals sound pretty sweet. You can increase the punch of a bass or drum by using a slower attack but longer release. You can kill a transient with a high ratio, low attack setting.


An Expander is basically the opposite. The controls are pretty much the same but instead of making the sound quieter, it makes the sound louder past the threshold.

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A compressor is typically used before the Pre-Amp in the chain.  I've found that a small amount of compression before the Pre-Amp and another after the Power-Amp can be helpful.  The compressor after the Power-Amp tends to makes chording quieter while single notes are less affected.  It can help with getting single note leads to cut through without having to add boost.  It's a delicate adjustment so take your time.


btw - awesome explanation from BillBee on how compressors work.  Nice job...

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There's Gremlins in that there Device!!!! I love that picture, LOL and the Gremlins movies. :) Good One!!. Also Great post BB.

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from http://line6.com/support/topic/263-bass-patches-pod-hd-series/?do=findComment&comment=1148



Tube Comp
Based on the Teletronix® LA-2A® studio compressor, is a fat dirty sound that is supposed to be like a vintage tube/optical compressor. It adds a layer of subtle distortion, and pumps the lows. Seems to be one of the most prefered choices by the (M and HD series) users when using a bass (see talkbass link below).
(quote: "It also has the most gain of all the models, such that I had to set the output level at minimum in order to avoid clipping the rest of my gear. So when I used it to push a tube amp into overdrive, it sounded really terrific--but it was almost unusable with a solid-state rig due to the nasty clipping.")
The original LA-2A has 40dB gain.
The compression position on the compress/limit switch on the LA-2A (again, the original thing) is considered 4:1, but really the ratio will fluctuate depending on the source.The LA-2A has a release time which requires about 60 milliseconds for 50% release, and then a gradual release over a period of 1 to 15 seconds to the point of complete release. You may think of the LA-2A as having a “composite†release; made up of several stages. When compression is heavy and/or the signal has been above threshold for a long time, the LA-2A's release will be slower.

Vetta Juice
The ‘Juice’ in Vetta Juice comes from the 30dB of available gain in the LEVEL knob.
It’s got a fixed threshold of -40dB with the SENS knob varying compression ratio from 1.5: 1 all the way up to 20:1 (which is a whole heck of a lot). This combination of design features gives you the option of cranking the level enough to get some serious gain boost, or setting the gain lower and dialing up a smooth, clean sustain.

Vetta Comp
Vetta Comp has a fixed ratio of 2.35:1 with the threshold (that would be your SENS knob) adjustable from -9dB to -56dB.
Up to 12dB of gain available at the LEVEL knob.
In other words, turn the Sens knob ’til you like the way your signal’s compressed, then set the volume with Level.

Boost Comp
Inspired by* a MXR® Micro Amp but with compression and EQ added. (Quote: "It's funny to me that the Boost model has the most controls, when the pedal it was based on has only one knob.")

The Vetta and Boost have the most natural, flattish frequency response of the group, good for "general purpose" use (including for bassists). Of those two, the Vetta is basic and clean while the Boost allows some extra drive and coloration, as well as having two-band EQ.
The Vetta and Boost both have better lows than the Blue, and the highs are about the same as the Red; and the Tube has massive lows, and OK highs.

Just like the majority of other digital comps, the POD HD it's not so good at peak limiting. You can get some decent limiting in the Vetta Comp, with the threshold low, if your playing is steady; but its ratio is only about 3:1, so if you hit it hard and fast (e.g. with slapping), it will certainly not stop those peaks.
However, the Vetta Juice has a widely variable compression ratio and a extra amount of gain to boost.


Among these first four compressor models, my personal choice are the top three for use with a bass (tube comp, and both Vettas). The Boost Comp model, although it may be perfectly valid, adds too many unnecessary parameters (at least for my personal taste and needs), and I think it may be better to keep things as simple as possible at this point.

Regarding the rest of compressors included in the pod, we could simply discard them, being more suitable for use with a guitar:

Red Comp
Based on the MXR® Dyna Comp.The Red model rolls off the lows severely, but has fairly open and present highs. Clearly meant for guitarists who want a bright sound.

Blue Comp
Based on the Boss® CS-1 Compression Sustainer with the treble switch off.
The Blue model has a little better lows, but the highs are muted; Clearly meant for guitarists who want a dark sound.

Blue Comp Treb
Based on the Boss® CS-1 Compression Sustainer with the treble switch on.


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