Compression vs. Limiting: A Question.

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Compression vs. Limiting: A Question.

Post by Judas Jetski » Sat Jul 14, 2007 7:29 am

OK, I have a question about limiting.

The other day I was re-mixing tracks from an old recording session to try to get used to some new gear & new techniques. I'd been using my new dbx160a for vocals (with great success) right up until this one particular song. When I got to this one particular vocal track, all the 160a did was make it sound like Play-doh. Just for kicks I tried running it through this Gates FM Limiter. Much to my surprise the FM Limiter sounded 200% better (that's right, 3x better) on this particular track. Crisper, brighter, and more natural. (My vocals on this track were at the very bottom of my register, where my voice tends to get a little weak.) But the FM Limiter only sounded better than the dbx when I limited holy hell out of the track & then jacked up the makeup gain. If I tried to use the thing with any subtlety it didn't help at all.

My impression is that the difference between compression & limiting is that limiting just lops off the peaks (leaving the rest of the signal alone) while compression reduces the peaks and at the same time boosts the rest of the signal.

Is there a technical difference between compression and limiting, or is this just a difference of common usage? It may just be radio-instinct to use a limiter without much makeup gain, and use a compressor to modify the signal more. It seems like that particular use of limiting would produce a much more subtle result. I know a lot of radio guys, so I may have somehow picked up some radio-guy thinking without really realizing it. (Not that there's anything wrong with that....)

So: aside from compression ratio, is there any real difference between a limiter and a compressor? Or is it that the FM Limiter simply sounds better in this application than the dbx does? Did I just compress holy hannah out of my vocals with that FM limiter, or did I do something else?

(btw, the FM limiter does not have a lot of variable parameters--just input level, output level, threshold and "limit/clip--limit--bypass;" I had this last control set for "limit/clip.")
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Post by drumsound » Sat Jul 14, 2007 9:12 am

The two terms are kind of interchangable. Many consider the difference in speed and often a fixed (high) ratio to be a "limiter" and a slower, more variable unit to be a compressor. Broadcast limiters are usually designed to set a ceiling that the signal doesn't go beyond. They can be fun for that reason. I was just messing around with my CBS Volumax last night. Like you said about your unit, its just is cooler when its really working.

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Post by dokushoka » Sat Jul 14, 2007 12:02 pm

Years ago, in school, I was taught that a limiter was anything with a ratio of 20:1 or greater. Who knows, though.

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Post by Judas Jetski » Sat Jul 14, 2007 1:58 pm

Yeah, see that's where my question is coming from. Everything I've *read* tells me that limiting is just really hard compression, and not necessarily with makeup gain involved. But everyone I've *talked to* seems to treat limiting as though it served a different purpose than compression.

That's where I got the idea that maybe it's just a matter of application--one does not usually limit where compression would do the job better.

I had pretty much decided that they were the same thing only to a different degree until I used this FM Limiter and got results that were spectacularly *better* than what I had anticipated.

But with all those buttloads of gain coming off the Limiter, I guess I was just using it like it was a compressor (which it is anyway). In my mind that would make limiting a variety of compression. Right?

This may seem like it's not really much of a question, but I want to make sure that I've got things right. I don't have the benefit of formal training, but I'd rather not live in ignorance all the same. :D
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Post by klangtone » Sun Jul 15, 2007 12:26 pm

Compression and limiting are basically the same thing. It's just considered limiting when it's really aggressive. But aggressive is not an exact term... so that crossover point is in debate, I suppose.

But using gain and limiting together is very common actually. That's a big part of mastering. Perhaps it's not called "make up" gain because it's more like you gain up the signal prior to hitting the limiter circuit. This causes your average level to go up and your peaks to really go through the roof. So the limiter squashes them down for you and you get a final output that has a smaller crest factor (ratio of peak to rms power) and is thus significantly louder.

The fact that you liked the limited signal more than the compressed signal could be due to so many factors. Just the fact that you're using two different pieces of gear is enough to make a big difference. So... like you said, you've had a lot of success using your dbx compressor. And now you experienced something better on a particular track with this limiter. As the old saying goes, just use your ears. Whatever sounds right, is right.

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Post by Judas Jetski » Sun Jul 15, 2007 2:19 pm

klangtone wrote:...sing gain and limiting together is very common actually. That's a big part of mastering. Perhaps it's not called "make up" gain because it's more like you gain up the signal prior to hitting the limiter circuit. This causes your average level to go up and your peaks to really go through the roof. So the limiter squashes them down for you and you get a final output that has a smaller crest factor (ratio of peak to rms power) and is thus significantly louder.


OK, that makes a lot of sense to me actually. Especially since I did have to jack up the gain at the board quite a bit to hit the limiter hard enough to make it sound like I wanted. I guess what I was doing was using the limiter in such a way that it functioned as a compressor (which is sort of what it is anyway). The fact that it gave me something I liked was maybe a mix of good luck and decent (if kinda crude) gear.

That sorta makes sense. It's about how I do practically everything else in life... upside down & backwards but usually with decent results.

I'll bet that one reason I liked it better on my vocals was because what the FM Limiter was doing was less intrusive than the dbx... and the fact that it limited the crap out of the peaks meant that I could let it leave the rest of the signal pretty much alone... maybe. I still don't fully understand "threshhold" function, so this actually may not be true. I had the "clip above" setting (that's threshhold, right?) set for the highest setting, 4KHz. The lowest setting is 10 KHz.
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Post by Mane1234 » Mon Jul 16, 2007 9:00 pm

I've always thought this was an interesting issue. I'm just now starting to use limiting so I don't have a very good handle on it by any means. Like others I always thought of it as hard compression but I never thought about the lack of make up gain and how that would effect things...I've started using one in comparison to compression across a mix buss to see the differences but I haven't listened enough to come to any conclusions yet. I was looking at a picture of the 160A and noticed those settings on the ratio knob that were past the 10:1 setting. I'd guess those are the limiter settings for that unit. Have you tried those in comparision to the Gates? I'd be curious to see what the difference is. I'd think as far as what the Gates did for you vocals you can't rule out the circuitry as having some role too. I couldn't find a picture of the Gates so I'm not sure what all kind of knobs it has.

Let us know what you keep finding out.
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Post by skinsincyn » Tue Jul 17, 2007 8:06 am

I myself have had a difficult time getting my head around the differences between limiting and compression. But think that I've finally worked it out...

Technically, as was said earlier, limiting has a higher ratio and faster attack/release times than compression.

The trick is to think of it like this: what would you want to put your beautiful, pristine recorded track through? An aggressive processor (limiter) that significantly reduces the level of everything it touches (threshold/high ratio), really, really quickly (attack/release)??

Or, would you rather run that nice, pretty track through, a more gentler, subtle processor (compressor), that somewhat reduces (threshold/ratio) the level of everything, but gradually (attack/release)?

I mean, it's not a rule, but that's what those tools were invented for. The 1176 attack times are in MICROseconds! Your brain can't perceive microseconds. So if you use it "correctly" you can reduce extreme transients (snare drums?) almost imperceptibly.

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Post by Judas Jetski » Tue Jul 17, 2007 2:00 pm

skinsincyn wrote: The trick is to think of it like this: what would you want to put your beautiful, pristine recorded track through? An aggressive processor (limiter) that significantly reduces the level of everything it touches (threshold/high ratio), really, really quickly (attack/release)??

Or, would you rather run that nice, pretty track through, a more gentler, subtle processor (compressor), that somewhat reduces (threshold/ratio) the level of everything, but gradually (attack/release)?
Don't forget that the FM Limiter sounded better than the 160A. Not better as in "worse in a cool sort of way." Better as in "more natural, clearer, and with less of a sonic footprint." In retrospect think what I was doing was hitting the parts of the signal that needed compression hard enough & early enough that I didn't have to do anything to the rest of the signal. It seems counterintuitive, but I think by using a more extreme form of compression I was able to alter the track less overall. Sort of like using a really hot soldering iron for sensitive electronics. If you go too far, you'll melt something you didn't want melted, but if you're judicious in its use you really have less chance of frying something than you would if you used a cooler iron because all the heat will be localized. Does that make sense?

I am also willing to bet that the FM Limiter was actually a pricier piece of gear to buy new than the dbx 160. That could explain the difference right there. Not that price point magically increases a piece of gear's quality...but I have to wonder if the Gates piece--designed for a specific application--might be outclassing the more generalized dbx.

Um I should also point out that the FM Limiter has a 3-way release time knob & VU meter so I had some idea what was happening to the signal & could adjust release time to taste.

BTW Mane--I have yet to get anything useful out of the infinity:1 and beyond settings on the 160A. But then I'm just getting a handle on compression & its manifold splendors...
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Post by joel hamilton » Wed Jul 18, 2007 8:50 am

Some random thoughts....

Nobody has mentioned the knee.

A crucial aspect of compression and limiting.

Every unit sounds different, every source is different...

A soft knee limiter is a compressor at low level.

A hard knee limiter is what people seem to picture limiters doing.

A soft knee compressor can limit at the top of its gain reduction cycle.

a limiter can sound subtle.

a compressor can sound drastic.

a compressor can hold a musical track to a specific level, or it can let it move.

A limiter can do the same.

The knee drastically changes the response of a limiter or a compressor.

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Post by SpencerBenjamin » Wed Jul 18, 2007 12:40 pm

You also mentioned the song was in your lower register. Compressors can distort on bass signals, although i think you'd have to be in four-balls territory...

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Re:

Post by buenavista » Mon Dec 31, 2018 11:26 am

joel hamilton wrote:
Wed Jul 18, 2007 8:50 am

Some random thoughts . . .
I spent the better part of the morning scouring the internet trying to get a grip on "knee" and how I might use it. This blurb was by far the most insightful and illuminating. Definitely a "light bulb" moment. Thank you.

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Re:

Post by Magnetic Services » Wed Jan 02, 2019 11:42 am

joel hamilton wrote:
Wed Jul 18, 2007 8:50 am

Nobody has mentioned the knee.
Exactly what I was going to say. Limiters typically have a much steeper knee than regular compressors, in addition to higher ratios and faster attack times. Instead of the compression gradually becoming more pronounced as you approach the threshold (like, say, a vocal compressor), it will engage fully right when you hit the threshold.
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Re: Compression vs. Limiting: A Question.

Post by vvv » Wed Jan 02, 2019 12:58 pm

As a practical matter, lemme note that, IME, software limiters can be near-transparent with numerous adjustable parameters, including "look ahead". (The limiter in Cool Edit a/k/a Audition is pretty amazing for that.)

Hardware limiting, IME, (and I've only really used smashing compressors, not dedicated imiters) is much less so.
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