Other Equipment

Daddy’s got a squeeze box: the big COMPressor COMParison.


What this post is: first, a discussion of what compression is and how it works, touching on studio compression and focussing on compression as a guitar effect.

Second (and most importantly), an extended audio comparison of five guitar stompbox compressors: original MXR Dyna Comp, DOD Milk Box, Jangle Box, Barber Tone Press, and the obscure Stigtronics Compressor (an enhanced Ross clone).

Why you might want to read it:
A, you're a relative newcomer to compression or a complete skeptic, and you want to know what it's about.

B, you're an expert and either want to challenge what I have to say or collaboratively correct and expand on it.

C, in either case, you want to compare the performance of these compressors. (To get straight to the sound samples, scroll way down.)

D, you don't mind my playing.

Why you might not want to read it: you don't care about and will never care about compression; you already have the ultimate compressor and have more important things to do with your time; my posts are way too long; you hate my playing.

Folksy introduction to goals, considerations, and results. Conceptually, the shootout is simple: play the same guitar material through several different compressors, at a couple of different settings, and record the results – so we can compare the performance of the compressors.

Hardest shootout I've ever attempted.

I intended to include enough variety of guitar techniques to cover the various effects compressors can have, which differ with pickups, pick intensity, effects, musical application, and compressor settings. It had to include single coils and humbuckers, light and heavy fingerpicking, clean chording, crunch, fast and slow lead both clean and dirty, etc. It was a challenge to come up a program covering all that.

To keep the comparison useful, the program had to be iDENTical through all the compressors. The solution was to play into a looper pedal first, then feed the signal chain from it. I didn't want to try punching in or patching it together in the looper, so I had to play the entire program acceptably in one pass. Since I'm lucky to play for 2 or 3 minutes without embarrassing myself technically, it meant lots of takes.

The final bit came together in a night, but I've been working at it for weeks. Then I changed the program at the last minute anyway.

Worst, when I was done I realized I'd left out two most typical compressor applications: clean chicken-pickin' and endless lead sustain.

Nonetheless, there's still plenty here to listen to: approximately four minutes of music employing various techniques, played back "naked" (with no compressor), then at two different settings through each of five compressors. That's a total of 11 tracks, and 44 minutes of compressor madness.

Not for the faint-of-patience.

Production Protocol
Signal chain: anonymous electric guitar --> Boss RC-20XL Loop Station --> Boss BD2 Blues Driver (Keeley mod) --> Fender Concert tube amp. Recorded at 16" from the amp by Edirol R-09 stereo "24-bit WAVE/MP3 Recorder" as 192k mp3 files.

Volume and tone pots on the guitar were wide open throughout; only pickup selections were changed. You'll hear all the switching. No settings were changed on the Blues Driver, at the amp, or on the recorder throughout.

After the program was played into the looper, it was used as the sound source (instead of live guitar) for the compressor tests. The dirt pedal was stomped "manually" every time (and not always at the same time).

The compressors were swapped into the same position in the signal chain one at a time (they were not all connected simultaneously, though that might be fun). Each got two passes, first with subtle settings and then more extreme.

The mp3 files were opened in Audacity on the Mac, and trimmed at front and end for consistency. The files were normalized to -1.5dB peaks so that all volume differences in the files result only from the performance of the compressors.

About Compression
Seems whenever there's a discussion of compression in a mixed audience of guitarists, there are some who have a lot of experience with it and some with none. Everyone knows what a distortion pedal does, but, as a more transparent effect, compression is less well understood. Part of the purpose of the exercise is to clearly demonstrate what a compressor DOES (by OVERdoing it), as well as how compressors can be used to improve tone without being glaringly obvious.

A micro-overview of compression might get us all on the same page. Parts of the following are intended for compressor newbies; other parts are for old hands. I mean to insult neither. Take or leave any part of the discussion for what is useful to you.

In the simplest form, compression is simply automatic volume control. If you had an assistant with impossibly fast and precise reflexes, and you could assign him to watch a level meter and make sure your signal never went above "X" on that meter, he would "ride the gain" on the channel and "compress" your loudest peaks down to your limit.

If that was ALL he was doing, he'd really be acting as a limiter (which is related to, but not the same thing, as a compressor).

Only he can also take the extra energy from your over-limit peak and save it to release as your note falls below the limit, pulling that level up – providing a more consistent level throughout a performance.

In fact, what if you could also have him make sure your level never fell BELOW "X" on the meter, no matter how lightly you picked? Technically, he'd then be operating as an expander. (Another related device.) And, again, he would serve to provide a more consistent level.

On the positive side, your magical golden-eared, sharp-eyed, instantly-reflexive assistant could help you stay consistently audible throughout a performance, without ever overbearing, unintentionally blurting or whispering a note, or getting too quiet.

On the negative side (depending on how you look at it), he's limiting and compressing your dynamic range.

Both things are true.

In practical application, most studio rack-mount compressors – and all guitar stomp-box compressors I know of - provide all these functions together: limiting, compression, expansion. They can boost low-level signals and squash high-level signals, and because of the design of their control circuits, they often do these things interactively. More about the control circuits in a moment.

Transparent vs "Special Effect" Compression
But I want to think more about how compressors bring the simple concept of automatic level control into reality, and the way they sound AS they do so – because understanding that is key to understanding why some guys like compressors, used in certain ways, and other guys don't.

Go back to your audio assistant. Let's assume he can't see into the future (some actually can), so he can't know when you're going to fall below or go above the volume threshold you've set. He can only react when you do it. This means that, no matter how fast he is, there will always be a split microsecond (at least) where the guitar gets through at its uncompressed level, and then you'll hear the result as he twists the knob or pulls the slider to adjust you to the "right" level.

Obviously these adjustments will be more or less audible. He can be told to yank it down (or push it up) very suddenly as soon as a compressible event happens – or he can be told to do it more slowly and gradually. Remember too that he's saving the extra electrical energy from your "overs" and releasing it to raise your "unders." What if you game the results by really pushing the volume, so that you're practically ALWAYS over, so that you're distorting the input amplifier on the channel and no matter what he does at the output, you're clipping a bit – and so that when you DO fall back below the threshold, he has a lot of collected juice to release, and has to keep pushing the slider up to let it out?

These "artifacts" of the way compressors work, the audible effect of their chasing your level in order to control it, are what we hear when we do hear compression. And sometimes those are desirable. I'll come back to THAT in a moment.

First I want to say that sometimes we DON'T want to hear the effects of compression. We want our parts to lay in consistently, with even attack and a Chet-like smoothness, to be audible without eating the mix. Maybe we want a little more sustain at the end of chords and notes. We want sudden overs to be invisibly controlled. We want to shape the volume envelope of our sound without it being audibly obvious that we are doing so. We'll call this transparent compression. It's frequently what we want out of high-quality rack-mount studio compressors. Sometimes we want that from stomp-box compressors too.

The truth is that most stomp-box compressors, and all but the best studio comps, do not do their jobs entirely transparently. Besides sometimes making it obvious that levels are being adjusted on the fly, they also have a subtle, grainy, fuzzy overtone especially at extreme settings. They can filter out highs. These are not usually desirable "artifacts," but they are usually there. Suffice to say that if we're after transparent compression, we'd rather not hear them.

But now let me come back to those times we want obvious compression. We want the effect, we WANT to hear magic fingers pushing and pulling the volume, pumping the channel. This is generally the domain of stompbox compressors. Most compressor-freaks are attracted to the rubbery squeezy sound of extreme compression before we appreciate its more subtle and refined uses.

All well and good. Distortion was not originally a sought-after "good thing" in the performance of audio gear, but we've learned to use it musically, seek it, and love it. Compression was originally designed just to squeeze big sound into small signal containers (like mechanical records and tape); during WW.II, it also became useful to keep voices in an audible range during radio and signal broadcasts. Originally, no one was interested in the accidental side effects – that we could hear the volume changes as they happened.

Audio engineers and producers originally used compression as transparently and INvisibly as possible. As the 50s wore into the 60s, though, some heard musical value in more apparent, even extreme settings. Studio compression is crucial to the sound of 60s pop. And it was during the mid-late 70s that special-effect compression was designed "down" into stomp boxes specifically for guitarists.

What ARE those special effects, and what do you listen for? Always, listen for the attack and decay characteristics of notes and chords. A very compressed note will have a quick pop at the beginning, then a sudden "suck" down, and usually a quick swell up at the end as well. A very expanded note will sound very faint at first, then gradually (or quickly) swell up "artificially."

Listen for chords that keep swelling as they ring, while they should be decaying, that seem to feed back into themselves and just keep growing.

Listen for long held lead notes that seem to sustain forever. These are the kinds of effects that more gain can produce – but compressors can produce them without saturation or the grainy fuzz of distortion.

Notes with unnaturally percussive, clicky attack are compressed.

Listen for phrases where the attack of every note seems overly and supernaturally cleanly articulated – and phrases that sound, from the articulation and tone, as if they are being played very lightly and softly, but which are as audible as if they were played loudly. At the other end, listen for notes whose tones sound like the strings are being ripped from the guitar, but which are no louder than the soft bits.

Ultra-even, very detailed and articulate power chords often owe a lot to compression. (Tom Scholz of Boston, and his Rockman, rely heavily on compression.)

Compressors are also very useful to hit a dirt pedal or the front end of an amp harder, and get the illusion of more volume, and more saturation, without shredding ears.

A very rubbery, elastic guitar sound is probably compressed, as is classic 70s-present Nashville chicken-pickin'. (I don't know about rubber chickens.) Funk guitar is often compressed. These have in common that a Telecaster, played hard, has a naturally compressed tone – but stomp boxes greatly magnify it.

Compressor Control
Studio compressors have a fairly consistent, and musically/electronically logical set of controls. Not all compressors have all of these (some do); most have most. (And this is a very rough overview, provided only because it breaks the "steps" of compression into logical components.)

• input gain: to adjust the input, either simply for signal matching or to force the device to compress the signal more or less
• threshold: the level at which you want the device to start expanding or compressing; usually expressed in dB
• attack: how quickly the compressor reacts when it reads a signal either falling below the threshold to be expanded, or above the threshold to be compressed; usually in ms
• slope/contour: related to attack, but controlling how gradually and consistently level is adjusted from the threshold to the target level; also called "knee"
• ratio: how exuberantly the expander amplifies a qualifying signal, or how hard the compressor squeezes it; expressed in ratios from 2:1 to infinity:1. (I've always thought "infinity" was probably more a theoretical ideal than something a mortal electronic circuit can deliver. Joe Meek excepted.)
• release: how quickly the device lets go of the signal when its input returns below the preset threshold; also in ms
• output gain (also called makeup gain): the output volume of the device, usually to bring the volume of highly compressed signals back up to the level they would have had without compression
Guitar compressor designers and builders have reached no similar consensus about what knobs ought to be on their boxes, or what exactly those knobs do. They know that guitarists quickly glaze over if there are more than two or three knobs to deal with, so they combine various sets of the above functions in the action of a single knob. The characteristic sound of different compressors result from just HOW the functions have been combined.

Each classic design takes its own approach, and there is no consistency in nomenclature. Sometimes you don't know WHAT the hell they mean by the label till you twist the thing. In general, though, one knob is usually a "compression amount" control, and another is overall volume.

Because studio compressors have such a complete complement of controls, it's possible to make different brands "sound" very similar to each other (especially the more "transparent" ones). Guitar compressors, on the other hand, embodying their designer's decisions on our behalf, sound as distinct from each other as dirt boxes.

It follows that some excel at some things, and others at different things. And past the seemingly requisite two knobs, it's the additional controls on various stomp compressors that dial in their unique capabilities.

OK, meet the contestants.
Some of the compressors in the shootout tend to be pretty obvious-sounding; others tend to transparency; all will operate across at least a range of that continuum. They range in price (new) from 50.00 to 225.00. All are available today.

And a few words about each one. But not about their SOUNDS – you'll make up your own mind about that.

MXR Dyna Comp: one of the first mass market stomp compressors (along with the Orange Squeezer), and still arguably the leader in the market. The first version had "MXR" in script, and is more highly prized by pedal freaks. The next version has "MXR" in block letters, and that's the one I've had since 1979 (and for about 10 years, if I was plugged in, it was on). Controls: Output, Sensitivity.

(The first Dan Armstrong Orange Squeezer, circa mid-70s, wasn't really a pedal, just a small box, and had NO knobs. On or off, baby. But it became a classic effect all the same.)

DOD FX84 Milk Box: as many knobs as a boutique job, but at popular prices. The first version called the controls Quarts, Cream, Pasteurization, and Spill; the manual revealed the code, and later versions are labeled: Level, Compression, High Expansion, and Attack. The high control is useful, as it lets you bring back the high-end content that stompbox compressors often lose. On the second clip of the Milk Box, below, I played with both the High and Attack controls as it played.

Jangle Box: the most recent design here, and the darling of the Rickenbacker crowd. A good all-round compressor, its main trick is its "bright/dark" switch, which re-eqs the pedal to accentuate or mute highs. Most guys use it to push the highs, and it uncannily reproduces the EQ and compression used on McGuinn's 12-string on The Byrds' hits. If that's what you're after, there's nothing better – and you get a competent compressor in the bargain. Controls: Gain, Attack, Dark/Bright. On the second Jangle Box clip, the bright control is alternately engaged. You won't be able to miss it.

Barber Tone Press: a relatively recent design, the TP includes – along with the main controls Volume and Sustain – a clever Blend control which mixes the compressed signal with a variable ratio of the unprocessed signal, passed clear through. One of the dead giveaways of compression is the percussive suckdown at the beginning of the note. The Barber lets you mask this with the unprocessed tone – which then decays and lets the articulation, smoothness, and sustain of the compressed tone swell up through. Pretty smart.

Stigtronics Compressor. The other early leader in stomp compressors was the Ross (the MXR is actually based on the Ross, but outcompeted it in the market). Ross went away fairly early in the game, and now the classic blue/gray Ross design is the basis of most boutique and clone compressors. This particular version is from a small builder in Bloomington, Indiana. I've tried Mike Stiglitz's dirt boxes, and they all impress me; I was anxious to get his compressor next to these others. I plugged his in first, and lost about three days just playing through it. I didn't want to unplug it. It's a first-class Ross-inspired design to which he's added an attack control. In short, I think it's a great box – amazingly clean and transparent in tone, but pumpy enough in effect. Easily the equal of anything here. Controls: Volume, Sustain, Attack.

Random Notes about the program material.
One of the functions of stompbox compressors is to boost low-level signal. I've left a few seconds of dead air at the beginning of each clip so you hear how much "noise" this adds when there's no signal at ALL. (Natural by-product of compression, just part of the package.) By the same token, switch clicks and other low-level noises are sometimes boosted as well; you'll hear that in the clips.

I purposely alternated both "too light" and "too heavy" playing in the program in order to demonstrate the compressors' action under those conditions. The inconsistent and extreme dynamics are intentional, as are too quiet and too loud passages.

Finally, the audio clips!

Uncompressed original signal.
Dyna Comp, light compression.
Dyna Comp, heavy compression.
Milk Box, light.
Milk Box, heavy.
Jangle Box, light.
Jangle Box, heavy.
Tone Press, light.
Tone Press, heavy.
Stigtronics, light.
Stigtronics, heavy.

What compression looks like.
(You can click the pics to hear the clips; right-click or command-click to open the clips in new windows and keep the pics onscreen.)

Pics of the compressors in action on this bit of music. The timeline is across the top of the screen captures from Audacity; if you play one of the clips and watch its elapsed time in your audio player, you can track the progress against the timeline and see how the compressor tracks and modifies the dynamics of the material.

Simply by comparing the uncompressed original to any of the compressed programs, you'll see that, in general, quiet bits are boosted and loud bits are squeezed. But the differences in the way the compressors respond to the same material are pretty dramatic.

And that's all I have to say. Time to decompress.

But what guitar did I use?


Oh yeah. What they look like.


DUDE - you're out of your smurfin' mind!:grin:

Nice job, accurate & complete info. Ummm, my thoughts?

You should be paid for these shootouts!!!

As always, well done, Proteus.:grin::grin:

I luvs my TP!


Another masterpiece, Proteus! And, by the way, were you surprised by anything from this shootout?


This is exactly what I have been looking for. I had been using a Monte Allums modded Boss CS-3, but it was too "special effect" ish for me. It will go up for sale, as many guys find these cool and useful. Now, I've got a used Guyatone ST-2 for $30 that has a switch that belends in an equal amount of "clean" signal with the compressed signal. It sounds fantastic! Hence, the Barber Tone Press would probably appeal to me.


This shoot out was extremely timely for me. Thanks Proteus - you made my short list shorter!


The guitar sounds like a hollow-body with single coils. We all know you have a Dyna CC, and you probably still have the DSV. They seem like likely candidates, with the DSV seeming slightly more likely. For some reason, though, after checking out the old surf guitar shootout, I think it might be the Charvel Surfcaster. I didn't listen to the samples again, though - that guess is on the basis of looks alone.


You should add an optocompressor to the list for the sake of completeness. Something like a Diamond or a Demeter...


I should have, ggb. I love optical compression...just never had it in a commercial stompcomp.

I DO have an optical another local guy built, and should have included that in the comparison. I still have the program material in the looper, so I can add that one when I get back to the studio.

Have you played the Diamond or Demeter? I've liked what I've heard of Diamond pedals so far.

I would also have liked to have one of the enhanced boutique Ross clones, like the Keeley, just for completeness. It's hard to have one of each!


Is there an abridged version...

Very nice job.


i've never liked compression, and, after listening to those clips, i still don't. out of those, the only i might consider would be the Janglebox, not because i'm a fan of Roger McQuinn's "jangley" guitar sound (The Byrds didn't start getting good 'til they abandoned jangle for twang, anyways!), but because a lot of other music i love has that same compression sound (didn't everything from the '60s, more or less?) still, The Janglebox didn't get "it" that much better than the others, and i find that cranking the pickups right up to the strings, and running 'em through a Vox, gets me "close enough" without compression!


Curt, just start at the sound samples.


Proteus, you've outdone yourself yet again! I know you said this was your toughest shootout to stage, but you've taken that wonderful empiricism we know and love to another level entirely with this one - waveform comparisons, even!

As one who's very unacquainted with compressors, this was very helpful. I think the Barber is my favorite, and I have a slight suspicion the Stigtronics might be a modded kit build from Build Your Own Clone. If it is, that speaks very highly of not only your builder friend, but the value of the BYOC kit builds.


actually, just for fun, i plugged my most "jangley" guitar (a Stratocaster, on the bridge pickup) into my computer, loaded up Garageband's "British Clean" amp model (everything on 10, except for the "pre gain" on 5), and selected the compressor preset "Electric Guitar More Attack." i did actually prefer the sound with the compressor! oh well. what do i know, anyways? besides, while those settings gave me tons of "jangle", the sound wasn't really anything i'd ever want to use seriously, probably…


This wasn't intended to be such a big project at first, seemed it would be so easy. It just grew. So I'm glad it's proving useful to some, and thanks to all for the positive feedback!

Ty, I think Mike Stiglitz is building from the ground up (though I'm not sure).

Stigtronics site.


I used to own a Diamond. Excellent pedal and dead quiet at all levels of operation. The tilt EQ is really useful as well. Also, their support is great.

I just find myself more comfortable with no pedals at all these days. The Diamond is the only compressor pedal I'd use if I rejoined the Floorboard Army.

P.S. This bad gateway thing is intensely annoying.


googoo, I'm just too curious, and will probably have to try one of the Diamonds. The combination of optical response and the shiftable EQ curve is too much to resist.

gman: DUDE - you're out of your smurfin' mind!
I am.

You should be paid for these shootouts!!!
I should, but wouldn't that sully my amateur standing?

Ric12string: And, by the way, were you surprised by anything from this shootout?
I haven't listened to the clips except in a functional way to edit them, so I don't know! Visually, I'm surprised at how massively the Jangle Box fattened the waveform. Subjectively, it doesn't sound that extreme.

I emailed Mike to check on the kit-build-mod concept; I really didn't know for sure.

He says:
I do build these pedals from ground up! All one has to do is open the pedal up and look. Other popular boutique compressors are closer to a Ross than mine. I spend many hours on R&D when developing new pedals ... listening as a musician who played full time and still plays a lot. '

I've also attended Purdue for three years of Electrical Engineering and have worked for many years as a technician.

Mike also provides some useful pedal development history, making the point that many commercial products use previous units as starting points, then mod and enhance:
Ross Compressor - modded Dynacomp
DOD 250 - modded Distortion +
Boss Super Overdrive - modded Tube Screamer
Fulldrive - modded Tube Screamer
DOD 201 Phaser - modded MXR Phase 45
Boss CS2 Compressor - pretty much a Dynacomp with a different chip

I've only met Mike a couple of times, and he seems a great guy, but we're not old buds or anything, and I'm not shilling for him.

That said, he has a stellar reputation as the go-to guy for amp repair among area pros, and players who could use anything on the market are choosing his compressor and dirt boxes. They seem to have their own character – very evolved, well-sorted, beautifully voiced.

So I guess the surprise to me, Ric12, came more out of preparing the shootout than listening to the clips – and that is that the Stig is such a great pedal.

seadevil: The guitar sounds like a hollow-body with single coils. We all know you have a Dyna CC, and you probably still have the DSV. They seem like likely candidates, with the DSV seeming slightly more likely. For some reason, though, after checking out the old surf guitar shootout, I think it might be the Charvel Surfcaster. I didn't listen to the samples again, though - that guess is on the basis of looks alone.

Not quite a hollowbody, but at least semi. Not a Gretsch. Yes, single coils...sorta. And not the Surfcaster, but at least partially trans-orange, like it was.

It's a secret guitar.

Proteus said: Ty, I think Mike Stiglitz is building from the ground up (though I'm not sure).

You're absolutely right, and I was WAAAYY off the mark... the BYOC kits based on the Ross are a 5-knob version, so I couldn't have been more wrong in my initial post.

My simultaneous apologies and congratulations to Mr. Stiglitz, as he's definitely onto something good with that pedal!

Proteus said: I emailed Mike to check on the kit-build-mod concept; I really didn't know for sure...

I made my previous post before scrolling further and reading this one, and now I feel even worse for my pedal faux pas!

I may have to buy one off your friend Mike just to mend fences! :nice:


No problem, Ty; I know you were just speculating, not making dire accusations. I didn't know on what basis – you've cleared up that you were misremembering the config of the BYOC comp kit.

In any event, no harm done, no need to feel bad. Now we all know more about all the compressors and their builders than we did.

I hadn't realized the BYOC had FIVE knobs. Do you know how irresistible that is to me?


Excellent Proteus. Probably the clearest and most succinct article I have ever read on compression. Being a rhythm guitarist I don't utilise it on stage, but only use it for recording - and whilst I know why I use it for recording instruments & voice and what it does for a recording the "technical" side always rather escaped my understanding. I therefore only ever used the presets on my TA Fatman valve - mono studio comp. Following your article I will now try it's manual adjustment settings.

By the way - "Guitarist" magazine should sign you up to write the occasional article!


Proteus, you should publish a gretsch book with an attached audio CD. I have almost given up on doing sound clips of stuff anymore since you have just about done everything there is to be done in the entire world of gretsch, or compressors, or bridges, or..... lol

Nice job. I know how to use my compressors and if I had to recommend just one effect for a home studio, a compressor would be it. Sure, it's not flashy like reverb or delay or phaser or flanger, but it's what sets your recordings apart from the amateur sounds of most people's home studio recordings. The trick is to compress to impress, not over compress. Overcompressing will make your mix sound squeezed and lifeless with no dynamics or fun-o-matic sound.

I appreciate what you do Proteus!

Proteus said: Visually, I'm surprised at how massively the Jangle Box fattened the waveform. Subjectively, it doesn't sound that extreme.

I think it DOES make quite a difference. Around 2:00, where the overdriven sound starts, compare that part to some of the others. The JB makes it quite a bit thicker!

Thanks for the great shoot-out (again), Proteus! Sometimes I think you're an undercover Gretsch guy, doing all that stuff on the GDP... Either that, or you MUST have a lot of free time and one VERY analytical, inquisitive and research minded brain... :grin:


Many thanks for this Proteus. Your selfless contributions to GDP (and maybe the world in general) are an inspiration.

Proteus said: In any event, no harm done, no need to feel bad. Now we all know more about all the compressors and their builders than we did.


The pedal lineage you posted is pretty interesting, to see who begat what tone. I knew the 250 and MXR were very similar, circuit-wise, but didn't know the MXR was a literal jumping-off point.

Proteus said: I hadn't realized the BYOC had FIVE knobs. Do you know how irresistible that is to me?

Yeah, they have some crazy stuff. I've been eyeballing their Rat clone for quite a while, now. I even had the crazy notion of building their Rat, TS-808 and MXR Distortion+ circuits into one big uber-box, but I like to think I'm pretty honest with where my limits are, and that'd be way above my pay grade!

Is there a-soldering in your future, perhaps?

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