Just boosting the volume will not, by itself, alter the nature of sound. It's only when you distort the audio that new harmonic and inharmonic components are added that can range from pleasant enrichment to harsh annoyance.
 
A limiter by nature is a distortion device. Clever designs can mitigate or disguise the distortion, but they all distort and they all add something new to the sound. This is true for both software and analog limiters. The only way to avoid that completely is to not use a limiter at all.
 
The difference between digital and analog devices is that digital processes can only mimic the way analog amplifiers naturally saturate. You have to really drive a vacuum tube hard before the distortion becomes unpleasant, and as it transitions into unpleasantness it does so in a gradual way. With digital devices, the onset of unpleasantness is abrupt and profound.
 
Another difference is that analog devices are simpler, with fewer options. They're easier to understand and use, and more difficult to abuse. Digital equivalents tend to offer many options, some of which are dangerous. A tube device will be designed to not react fast enough to do the worst kind of damage. But software can react to individual samples if you tell it to. At 44.1 KHz, that's about 50 times faster than the threshold at which you're likely to start causing audible distortion.
 
So when I hear somebody say they get much better results with outboard gear, my first thought is that they were probably mis-using their digital gear in the first place.

Pro-L has some whacky labeling.
 
The "Lookahead" parameter controls the limiter's attack while the "Attack" parameter controls the limiters hold.
 
The manual uses the term "transparent" a lot, I have no idea what that means these days.
 
Out of all the brick wall limiters I have tried, I think Voxengo Elephant has the tricky stuff figured out.
 
Limiting is not limited to the idea that a strong audible bass has more energy than an audible upper midrange... there is also the idea that moderate upper midrange can sound like a ice pick in your ear if it isn't acknowledged and processed with the limiters algorithm effectively.
 
I don't think Pro-L sounds as *smart* as Elephant seems when it is processing a wide spectrum of full range dynamics. 
 
 
 
 
 
 
 

Yeh, Pro-L is a little obtuse. The first time I looked at it, my first thought was "why on earth does a brickwall limiter have an Attack knob?"
 
Then I figured out that the core of Pro-L's secret sauce is a transient detector, with separate algorithms for transients versus slow-moving values. The Attack control is really adjusting the point at which one algorithm hands off to the other. Make it short and you only process the fastest transients separately. Make it very long and you essentially bypass the transient processor, turning Pro-L into a generic limiter.
 
In Dynamic mode, Pro-L kicks in a transient enhancer in front of the limiter. Kind of like Dolby pre-emphasis but for dynamics. It's my favorite mode.
 
And yes, lookahead is a kind of a reverse attack setting. The shorter the lookahead value, the longer Pro-L waits before mitigating a peak. Longer lookahead values make the process more transparent. But I'm using "transparent" to mean you don't hear the limiter working, not in the way most of the kids over on KVR use the term to mean "still sounds OK when I turn it up REALLY loud".

When I use Pro-L for more than metering I use Dynamic mode as well. The best thing about Fab Filter IMO is the way the visuals work. Pro-C really taught me how to use a compressor and what each thing actually does. They are more than pretty, they show valuable information. I certainly love Fab Filter.

bitflipper
Then I figured out that the core of Pro-L's secret sauce is a transient detector, with separate algorithms for transients versus slow-moving values.

 
IIRC, Elephant has 8, maybe more of these algorithm choices.

Technically, so does Pro-L.

I went and looked at the details again. Elephant 3.1 has 10 styles of limiting that you can manually select.