Limiter Forms and Definitions

[Compyfox]

Dear colleagues - before you go haywire with the following question, please remember one essential thing: "there are no stupid questions, only stupid answers"

Since especially "beginners" might learn from the following discussion, let's try to keep it as simple as simple, please.



My question is simplistic, yet I still struggle with the understanding (for years now!) - especially if the terms seem to differ around the globe:

What are the differences in Limiters - and how are they defined?


I speak about Limiters in general, Brickwall Limiters, Maximizers and the Clipper. Please let me note down what I think of what is what and feel free to correct me at a later state. The only difference IMO between "soft" and "hard" is the actual used knee, else a limiter is in basic form a compressor with infinite:1 ratio.



Limiter (generic):
- basically a compressor with ratio infinite:1
- freely adjustable attack and release times (recommended ultrafast attack, medium release)
- freely adjustable makeup gain

Pro:
- keeps the signal from overshooting
- dynamics retained if moderately "limited"

Con:
- chances are the limiter misses certain overshots



Brickwall Limiter:
- basically a compressor with ratio infinite:1
- mostly freely adjustable attack and release times (see Limiter - generic)
- freely adjustable makeup gain
- look ahead function (also known as "pre-compression")

Pro:
- keeps the signal from overshooting
- catches even rouge peaks (hence the name "Brickwall") due to the look ahead mode

Con:
- dynamics can not be retained due to the look ahead mode
- only a small amount of makeup gain is recommended before introducing pumping/distortion to the signal (about 5dB max)



Maximizer:
- basically a compressor with ratio infinite:1 (can't be changed)
- fixed attack and release times (attack in microseconds, release moderately)
- Makeup gain corresponds to the input gain (e.g. -3dB threshold/input gain, automatic makeup gain of about +3dB)
- threshold is 0dBFS, unless the output stage can be adjusted to something like -0.3dBFS (like TLs Maximizer)

Pro:
- mostly only one to two faders for control

Con:
- instead of turning the "threshold" down, you "drive" the signal into the fixed threshold - a confusing concept at first
- dynamics can not be retained unless adjustments can be made to the response (attack/release)
- rarely control over the output limit (mostly set up at -0,1dBFS)
- mostly no control over look ahead time or release

Unsure:
- don't know if look ahead plays a part with this type of limiting




These are the three types of limiting I know. But I'm not too sure about the "Clipper". To my understanding, it's also a standard "limiter". But why is it that special? How is it defined?


Looking forward to your contributions.

[AL321]

My question is simplistic, yet I still struggle with the understanding (for years now!)

Me too! I wish someone could clear this up once and for all.

Here's the way i see it: when you push a limiter hard, it sounds like a compressor, just squashing everything smoothly. but when you push a maximizer, it just starts to distort. You don't really hear the compressor effect so much. I think the difference (just my humble opinion) is saturation. A maximizer uses saturation and mega fast attack/release comp to get the loudness instead of just compression.
An example of saturation in action would be the Fruity Limiter in FL Studio. Get your song loud and pumping with minimum attack/release. Now slowly turn down the saturation knob. You will hear it start to distort, even though the attack/release hasn't changed.


The confusion for me is the way people label things, and i also think that all good limiters do use some saturation to an extent, to get that volume pumping really loud.

[Kim Lajoie]

It's quite simple really.

Limiter: Compressor with very high ratio and (usually) very fast attack.

Brickwall limiter: Digital limiter with instant attack and infinite ratio. Stops digital clipping.

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

Clipper: Brickwall limiter with instant release. Causes audible distortion as a result of waveshaping.

Maybe I'll do a blog post on it going into a bit more detail.

-Kim.

[dark_virus]

- freely adjustable attack and release times (recommended ultrafast attack, medium release)

What would be a fast/medium/long attack/release? I never understood these compressor terms properly.

EXAMPLE: is a 100ms release fast or long?

[Kim Lajoie]

- freely adjustable attack and release times (recommended ultrafast attack, medium release)

What would be a fast/medium/long attack/release? I never understood these compressor terms properly.

EXAMPLE: is a 100ms release fast or long?

Short answer: it depends on the characteristics of the sound, and the behaviour of the compressor.

Slightly less short answer (with audio examples): http://kimlajoie.wordpress.com/2008/12/ ... ase-times/

-Kim.

[dhalfen]

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

Mostly "marketing magic!"

I was looking for a good "audio wizard" pic, but Google failed me.

Essentially, this is just a "different way" of looking at the purpose of limiting - let's dust off the ol' "glass half-full/half-empty" perspective:

Half-full: You're looking down at the surface of the water from the rim. (Keep the water below the rim.)

Half-empty: urrrr innnn ehhhhh waaaaaahwherrrrrr llloooookinggg uuuuuuuub. (Raise the water as close to the rim as possible without going over.)

So, IOW, those who do "maximisers" are "all wet."

(Or very stingy with money.)

[Compyfox]

Thanks for joining the conversation, Kim.

Limiter: Compressor with very high ratio and (usually) very fast attack.

Well, everything above 10:1 is already declared as limiter, no?

Brickwall limiter: Digital limiter with instant attack and infinite ratio. Stops digital clipping.

So by instand attack, I think you mean attack in the microseconds range. But what about the constant "needs look ahead to be brickwall" I keep on hearing about through several boards? And does it really need to be digital?

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

I wouldn't say that it's magic, it's just a different concept.

Like I said - to my experience (and knowledge), a Maximizer is a set up limiter where you drive the signal into "compression" (or in case of very high/infinite ratio, into limiting) with the threshold set up at 0dBFS. The attack times can sometimes be switched, but are mostly at "very fast" (around 0,5ms to 1ms) or "instant" (microseconds). while the release is moderate (300-500ms).

"Maximizer" is a buzzword indeed, you try to "maximize" the loudness of the source material after all. Unless I misunderstood the concept.

Clipper: Brickwall limiter with instant release. Causes audible distortion as a result of waveshaping.

Ah, this clears the "to clip the peaks" thing - with the disadvantage to have a distorted signal (clipped) and a slightly pumping sound. Which is why such plugins are sometimes used two times in row to make this effect less audible.

Now everything falls into place again.

Maybe I'll do a blog post on it going into a bit more detail.

Why not elaborate more in here as well?

EXAMPLE: is a 100ms release fast or long?

As Kim said, it really depends on the characteristic of the compressor/limiter. If we talk digital, 100ms counts to fast->moderate. Moderate release is usually something around 300ms. At least if you go by the book (and there are a lot mentioning that).

A maximizer uses saturation and mega fast attack/release comp to get the loudness instead of just compression.

Uhm, I don't really think so in this case. All Maximizers I used up until this day rely on a fast attack and moderate/medium release to catch all peaks, but also to prevent the pumping effect (as is the case with TLs Maximizer by TbT Audio). It's not a 100% brickwall limiter (depending on the settings of course), but it's definitely no Clipper either.

The signal saturates automatically since it's driven into a certain theshold. And since that is usually the digital 0dB reference point, you get saturation. You can prevent this (to my knowledge) if you turn down the master output to (let's say) -0.3dB, and to turn down the saturation again, introduce "look ahead detection" (pre-comp). But you will miss out in terms of raising the loudness before it's distorting again. And that is usally within a 5dB range (see MPL-1 Pro from Kjaerhus)

I think the "maximizer" concept really comes from lazy engineers who wanted to have things simple (1-2 knobs), but with the best working settings for most program material.

The confusion for me is the way people label things, and i also think that all good limiters do use some saturation to an extent, to get that volume pumping really loud.

The saturation depends on the used internal programming and transfer courves. But yes, I agree that people like to label things in a crazy way rather than for what this tool really is.

[mauseoleum]

A clipper will limit the incoming signal (by clipping peaks), but it's not a limiter.

A clipper is recognisable by lack of any time constant vs. other "compressor-derived" limiter types, which all operate on the following principles:

- they have a gain cell that changes gain depending on input signal (usually peak) value
- said gain cell is controled via a derived envelope signal by using a rectification and a time constant
- the "limiter" circuit(s), in hardware, are often very similar to compressor circuits

A clipper, on the other hand, does not operate on a principle of gain reduction cell and envelope signal - it does not have any time-constant

- in hardware, a clipper is often depicted by a back-to-back zener diode pair and a current-limiting resistor
- there are other types of clippers, but the above one describes the basic mode of operation well enough

[Kim Lajoie]

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

Mostly "marketing magic!"

Sometimes it is mostly marketing, but I wasn't referring to that. By 'magic', I was referring to a collection of techniques such as adaptive release curves, multiple serial stages, blended clipping and gain reduction, frequency-dependent behaviour, multiband operation, oversampling, etc.

-Kim.

[Kim Lajoie]

Thanks for joining the conversation, Kim.

Limiter: Compressor with very high ratio and (usually) very fast attack.

Well, everything above 10:1 is already declared as limiter, no?

Roughly, yes. Ten isn't a magic number though. 8:1 can sound like limiting in some cases. In others it takes more than 10:1. One of my favourite compressors goes up to 1000:1.

Brickwall limiter: Digital limiter with instant attack and infinite ratio. Stops digital clipping.

So by instand attack, I think you mean attack in the microseconds range. But what about the constant "needs look ahead to be brickwall" I keep on hearing about through several boards? And does it really need to be digital?

No, by 'instant', I mean it really is instant. Any sample that exceeds the threshold is reduced. Lookahead isn't necessary, but is often implemented to reduce distortion. Without lookahead, a brickwall limiter will operate a bit like a clipper during the attack phase. Generally, brickwall limiters are digital, because you're necessary in preventing digital overs. They could theoretically be implemented in analogue, but there's not much point.

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

I wouldn't say that it's magic, it's just a different concept.

Like I said - to my experience (and knowledge), a Maximizer is a set up limiter where you drive the signal into "compression" (or in case of very high/infinite ratio, into limiting) with the threshold set up at 0dBFS. The attack times can sometimes be switched, but are mostly at "very fast" (around 0,5ms to 1ms) or "instant" (microseconds). while the release is moderate (300-500ms).

"Maximizer" is a buzzword indeed, you try to "maximize" the loudness of the source material after all. Unless I misunderstood the concept.

As I wrote above, my use of the term 'magic' isn't cynical - it's shorthand for a collection of signal processing techniques.

You're right that most maximisers are designed to increase gain (with a big input boost control), not reduce headroom. Unfortunately, most 'mastering' limiters are designed this way - it's not just tools labelled as maximisers.

Clipper: Brickwall limiter with instant release. Causes audible distortion as a result of waveshaping.

Ah, this clears the "to clip the peaks" thing - with the disadvantage to have a distorted signal (clipped) and a slightly pumping sound. Which is why such plugins are sometimes used two times in row to make this effect less audible.

Now everything falls into place again.

Mauseoleum is right that clippers usually aren't implemented in the same way limiters are. Clippers usually don't have a gain reduction circuit - their internal design is closer to distortion than compression. For the purposes of this discussion, however, it makes sense to describe their behaviour in terms that can be compared to limiters.

Maybe I'll do a blog post on it going into a bit more detail.

Why not elaborate more in here as well?

I use my blog so that my posts are easier to find and available to a wider audience.

-Kim.

[dark_virus]

EXAMPLE: is a 100ms release fast or long?

As Kim said, it really depends on the characteristic of the compressor/limiter. If we talk digital, 100ms counts to fast->moderate. Moderate release is usually something around 300ms. At least if you go by the book (and there are a lot mentioning that).

Thanks. That's exactly what I need!

[dhalfen]

Maximiser: Marketing term. No real meaning. Usually implemented as a blend of limiting, clipping and magic.

Mostly "marketing magic!"

Sometimes it is mostly marketing, but I wasn't referring to that. By 'magic', I was referring to a collection of techniques such as adaptive release curves, multiple serial stages, blended clipping and gain reduction, frequency-dependent behaviour, multiband operation, oversampling, etc.

Ah - you weren't being cynical!

But would you say that calling something a "maximiser" is mostly just a matter of changing one's perspective with limiting and clipping (i.e., instead of keeping below a line, you try to raise right up to a line?), or do these techniques achieve something "beyond" limiting?

(For that matter, could you recommend any good "maximiser" as a more-or-less-ideal example? I've always been under the impression that the terms really was just hoopla... )

[AL321]

The signal saturates automatically since it's driven into a certain theshold. And since that is usually the digital 0dB reference point, you get saturation. You can prevent this (to my knowledge) if you turn down the master output to (let's say) -0.3dB, and to turn down the saturation again, introduce "look ahead detection" (pre-comp). But you will miss out in terms of raising the loudness before it's distorting again. And that is usally within a 5dB range (see MPL-1 Pro from Kjaerhus)

Oh, i'm probably just talking nonsense. I know next to nothing about these types of mechanics. I just know i get my music louder when i use saturation. Just had another look at the Fruity Limiter. It doesn't need to be near 0db to distort without saturation (i had it distort at -10db), but i did manage to stop the distortion with a long lookahead, although the crazy pumping it created means i'll choose saturation over lookahead any day.

So why is it that some brickwall limiters just totally fail at bringing the volume up to commercial levels, if they are all doing the same thing? is it all down to the attack and release curves used?

[Kim Lajoie]

But would you say that calling something a "maximiser" is mostly just a matter of changing one's perspective with limiting and clipping (i.e., instead of keeping below a line, you try to raise right up to a line?), or do these techniques achieve something "beyond" limiting?

Unfortunately, most 'mastering' limiters work this way too.

(For that matter, could you recommend any good "maximiser" as a more-or-less-ideal example? I've always been under the impression that the terms really was just hoopla... )

Not sure what you're asking here. Can you explain a bit more?

-Kim.

[Compyfox]

A clipper, on the other hand, does not operate on a principle of gain reduction cell and envelope signal - it does not have any time-constant

Mauseoleum is right that clippers usually aren't implemented in the same way limiters are. Clippers usually don't have a gain reduction circuit - their internal design is closer to distortion than compression. For the purposes of this discussion, however, it makes sense to describe their behaviour in terms that can be compared to limiters.

Well, then how can it be described if we go by the definitions I started in the first post?

No, by 'instant', I mean it really is instant. Any sample that exceeds the threshold is reduced.

Funny though that some so called "brickwall limiters" work with microseconds, some even millisecond values to be called "brickwall". So what's the actual deal here?

If it's only a "brickwall limiter" if we go by two needed facts: being digital and sample based limitng, then why are so many tools called "brickwall limiter"?

Examples: Kjaerhus MPL-1 Pro, T-Racks 3 Brickwall Limiter (works with 0,05ms attack), Waves L1, etc.

Lookahead isn't necessary, but is often implemented to reduce distortion. Without lookahead, a brickwall limiter will operate a bit like a clipper during the attack phase.

So a "clipper" without attack/release, or nearly instant attack/release (microseconds again) is in basic theory a limiter with different knee values, no? (see T-Racks Clipper)

I use my blog so that my posts are easier to find and available to a wider audience.

Understandable, but isn't the discussion in here insteresting as well?

(For that matter, could you recommend any good "maximiser" as a more-or-less-ideal example? I've always been under the impression that the terms really was just hoopla... )

From personal experience:
George Yohng W1, which is a "clone" of the Waves L1 Limiter (which is known to be a "mastering limiter" or better said a "maximiser" as well)
TbT Audio's TLs Maximizer

Both are free, both count to the factor "maximiser". In theory, the T-Racks 3 Brickwall Limiter is a maximizer as well, since you "drive" the signal into the threshold rather than lowering the treshold and raising the gain again. Only that you have more control over attack/release values, and additional bonus modes (which doesn't save this one from clipping or pumping however, not even with the distortion prevention mode, which still causes hidden clipping).

Oh, i'm probably just talking nonsense. I know next to nothing about these types of mechanics. I just know i get my music louder when i use saturation.

This is an effect you get through the distortion of the signal. One way or another, you're adding harmonics that way, which tells your ears and brain "there is more to the signal, so it must be louder". It might however look different thought measurement tools.

Just had another look at the Fruity Limiter. It doesn't need to be near 0db to distort without saturation (i had it distort at -10db), but i did manage to stop the distortion with a long lookahead, although the crazy pumping it created means i'll choose saturation over lookahead any day.

As mentioned, the "look ahead" is there to actually prevent distortion. What the look ahead mode does is some sort of "pre-compression" before the actual compression. This however goes only well within certain dB ranges in terms of loudness raise. Kjaerhus' MPL-1 being the prime example... long lookahead, mild to no distortion whatsoever, but turn it up more than 3,5dB and it pumps like nobodys business.

So why is it that some brickwall limiters just totally fail at bringing the volume up to commercial levels, if they are all doing the same thing? is it all down to the attack and release curves used?

Somewhat yes. If you look at that way. Brickwall Limiters respond (nearly) instantly, meaning, they sqwash the transients as well. Normal limiters can be setup, so that the transients are unaffected but rather respond to the overall loudness, but to be clean of digital overshots, you need a brickwall limiter again in chain. Benefit: you can raise the crap out of your track with your prefered sound design tool (compressor), while keeping just the peeks in check with a nearly non-operating brickwall limiter.

So called "maximisers" usually do both (at least to my knowledge/experience). Or they use at least some specific settings for that purpose (specific ratio, different att/rel, special algos for analysing). "Brickwall Limiters" are only used while Mastering (actually Pre-Mastering as it would be called correctly) anyway, so a normal Limiter usually does the trick if we talk about individual channels.

One way or another, if you boost that much to get to mowaday consumer level, you "distort" the signal automatically. Take a look at the "Loudness War". Personally I try to now boost higher than 3-5dB at max if it's already within the K-System (a bit lower than K-14). This way the limiter doesn't degrade the signal as much.

But please let's not go there (talking about how to master, etc).