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What do compressors do? I'm looking at a Keeley one since it gets amazing reviews.
 

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Well the name kinda says it all. They squeeze or compress your sound. It works on the volume of the notes etc. It evens out the sounds of your notes, soft notes are raised in volume, loud notes are lowered in volume.

On a nice clean sound, a comp can really make things sound fuller and I guess you could say warmer. A lot of country players use a comp. Some metal players/shredders use/used comps to help bring out the lead tone. I remember back in the 80's alot of shredders who tapped etc used on to help keep the sound of their solos up because sometimes when you're tapping etc notes can be quiet etc.

They can thicken up chords as well. One thing to remember about a comp though, it is one of those effects where less is more. Too much comp and things start to sound goofy and rubbery, especially on the low end.

So ends my take on the compressor pedal.
 

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Ripper's description is pretty accurate. What it actually does is to gradually increase the volume of the note as it decays, which makes the notes sustain more.

There are different ways to use it depending on how you set the controls.


And a big thumbs up for the Keely. It's the best one I've used. It's really a nice sounding unit.
 

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Compressors reduce dynamic range - the difference in amplitude of the softest note to the loudest note.

Most do this by automatically turning down the volume of the louder notes at a set threshold and ratio, but there are also compressor/expanders that will also increase the volume of quiter passages at a set threshold and ratio. Different units have different compression technologies, and most have adjustable thresholds, ratios, attack and release times.

How a compressor is set up depends on the application and the program material. Inexpensive compressors (based on LED detectors) have a tendency to compress unevenly accross the frequency range, sometimes leaving the higher frequencies uncompressed while clamping down hard on the lower, more dominant frequencies. The resulting sound is not pleaseing to the ear and is what I would consider to be downright nasty. An EQ in the side chain (control signal path, not audio path) is required to smooth out the response of some compressors.

The best compressors (IMO) are tube compressors. If you have a tube amp and you play with two channels you can easily see the difference between a compressed and uncompressed signal by checking out the difference in dynamic range between a high gain sound and a clean sound. There is little difference in the volume between a lightly picked note and a more dymanic strum with too much gain. High gain tube amp users will often get complaints from soundmen that heir clean sound is way louder than their dirty sound, as the clean sound is not compressed.

Compressors are meant to be used sparringly, that is they are meant to react to the part of the signal that needs to be attenuated, not the entire program material. They should be transparent and lay in waiting until they are needed. They allow you more 'net' volume or more usable headroom through whatever you are using it on (if used correctly) at the expense of reduced dynamic range. I use them extensively in live sound to keep signals and the entire program material within the confines of the PA systems capabilities.

With all of that being said, I have seen compressors used in a more artistic way to create sound envelopes (attack is uncompressed but a hudge gain reduction following the attack giving a staccado effect or the opposite - no attack and ramping volume).

In my opinion, compressors are probably one of the hardest audio devices to get a handle on - I've seen some instances where the user cannot see any difference at all between a heavily compressed and lightly compressed signal (use the high gain two channel tube amp as a perfect example).
 

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Peavey Wolfgang EVH Wolfgang Charvel Style 2
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Hamm Guitars... glad you raised the point that compressors are hard to detect if you do not know what you are listening for. And as mentioned compressors need to be used sparingly. There is an amount of natural compression that occurs during the clipping of a signal... more gain more compression. Tubes do it best by most players accounts as they maintain a nayural organic warm quality to the compression.

Imagine a dotted line drawn horizontally on the bottom and a dotted line drawn horizontally on the top... these lines represent the max volumn of the sound wave. Between the two dotted lines is where the sound wave will travel... imagine a solid line in the middle this is where the sound originates from. If you know what a sine wave is then you have it half beat. A compressor moves the bottom and top horizontal dotted lines closer or further away from the solid line effectivly allowing more or less volumn. If the sign wave is allowed to peak within the limits of the top and bottom dotted line you will hear all the sound wave's volumn rise and volumn drop ( more dynamic ). If the top and bottom dotted lines are closed in on the wave to say the half way mark you will not get to hear all the volumn rise and drop you will hear a signal that is percieved as being more even in volumn levels ( less dynamic ). Sometimes you will hear the name compressor/limiter. Limiter is easy to understand with the discription I've given as the lines limit the sound wave.

See the diagram... http://www.barretteng.com/Images/Symble5.gif

sine wave... http://www.mckinneyhonda.com/graphics/honda_eq/imageinvert.gif

sine wave clipped ( distortion )... http://images.google.ca/imgres?imgurl=http://content.answers.com/main/content/wp/en-commons/thumb/6/61/400px-Clipping_1KHz_10V_DIV_clip_A_5ohms-1-.jpg&imgrefurl=http://www.answers.com/topic/clipping-audio&h=284&w=399&sz=28&hl=en&start=4&tbnid=i1Zcx4Nr_LOrSM:&tbnh=88&tbnw=124&prev=/images?q=clipped+sign+wave&gbv=2&svnum=10&hl=en

other usefull info... http://images.google.ca/imgres?imgurl=http://content.answers.com/main/content/wp/en/e/ec/Squarewave01CJC.png&imgrefurl=http://www.answers.com/topic/squarewave01cjc-png&h=442&w=600&sz=22&hl=en&start=4&tbnid=nuGbKzLC9_3D9M:&tbnh=99&tbnw=135&prev=/images?q=sine+wave+components&gbv=2&svnum=10&hl=en


Khing
 

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Explanations above are great, I'll just add my two cents about the Keeley specifically. If you're concerned about purity of your tone, I'd be wary of the Keeley. I know it gets great reviews, I bought one based on them, I hated the pedal. It instantly changed the sound of my whole rig when it was on. I don't just mean the compression. I've tried pretty much everything out there and finally landed on a Carl Martin Compressor/Limiter. It's perfect for me, it does studio quality compression/limiting in a stomp-box, and is 100% transparent.

Anyway, just FYI before you drop a load of cash on one, might want to find one to try out first. Though, to be fair, Keeley will refund your money if you're not satisfied.
 

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I agree with the poster above re: Keeley. It's a great pedal, but you need to know whether it's the one for you or not. The Keeley is from the Ross/Dynacomp family and they squash hard and quickly. I had one and barely used it. I got an AnalogMan Juicer, which is from the Orange Squeezer family, and liked it better. Recently, I bought a Diamond, which is the opto type, and I absolutely love it. I use it a lot now live. It's the most subtle type. The Keeley is not subtle at all and that's why I rarely used it (or the Way Huge...or the block logo Dynacomp before it).
 

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I have found the Marshall Ed-1 to be a great value compressor. if you aren't super concerned about price. The Carl Martin is hands down the best pedal compressor on the market
 

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I have found the Marshall Ed-1 to be a great value compressor. if you aren't super concerned about price. The Carl Martin is hands down the best pedal compressor on the market
...perhaps, but the blend control on the barber tone press puts it in a class all by itself.

-dh
 

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Peavey Wolfgang EVH Wolfgang Charvel Style 2
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Thats good to know aboutthe keeley... I would be looking for transparence and subtlety from a comp/limiter.
The Marshall ED tho good bang for the buck with interesting capabilities ie; you can compress the top or the bottom only and have the ability to mix the two... cool but changes the tone.

Khing
 

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Thats good to know aboutthe keeley... I would be looking for transparence and subtlety from a comp/limiter.
The Marshall ED tho good bang for the buck with interesting capabilities ie; you can compress the top or the bottom only and have the ability to mix the two... cool but changes the tone.

Khing
Solid gold comp 427

http://www.solidgoldfx.com/comp_427.php


I was talking to Greg Djerrhian about this one, and he has designed it to be quiet and transparent, and the price is very fair. I don't have one but he has made pedals for me before and the workmanship is second to none.
 

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Thats good to know aboutthe keeley... I would be looking for transparence and subtlety from a comp/limiter.
The Marshall ED tho good bang for the buck with interesting capabilities ie; you can compress the top or the bottom only and have the ability to mix the two... cool but changes the tone.

Khing

I think it's possible that other makes are more transparent than the Keeley, but it's important to clarify that the Keeley CAN be used in a subtle way. Frankly it's the only model I've ever kept on my pedalboard for more than a day. When I use compression I don't like it to be noticeable, other than the fact that sustain is greatly enhanced. The Keeley does this well.
 
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