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G-Con, if the limiter's gain reduction meter is showing no activity, then it means all the sounds coming into it are below the threshold. In your example, it means that only very infrequently are there sounds that are louder than -4.5dB.
In this case, setting the threshold there will act like a very clean volume control - the dynamics won't get affected if there is no actual limiting taking place.
In the analog world, you'd want to ensure that the sounds coming into the limiter are as hot as possible while still being clean, since analog gear sometimes doesn't have the best signal-to-noise ratio. So in that case, you wouldn't want your hottest sounds peaking at -4.5dB, you'd want to raise the individual tracks so you're close to 0dB (without clipping/distortion - though some analog gear distorts very warmly/ smoothly and imparts character, so once again, it's not a hard and fast rule)
But anyway - in the digital world, things are generally much much cleaner - the signal-to-noise ratio will generally be excellent - if you happen to be working at -4.5dB, then raising the level at the input stage of the limiter shouldn't introduce any audible noise at all. (It's very hard to hear sounds which are at -60dB, and 24 bit digital audio has a range of -what, 100dB, 120dB? I'm sure there are people who have that information in their heads, I'd need to look it up). In practical terms, there's no way that lifting the volume by 4.5dB at the input stage of the limiter will affect sound quality.
In other terms, you shouldn't be concerned about where the threshold of the limiter is per se. It may be at -3dB for one track, at -12dB for another track (though generally if you have a set workflow, your tracks will settle into a tighter range over time) If the incoming signal is quieter, the threshold will be lower, if it's louder, then it will be higher. What is of interest to you is once it actually starts showing some gain reduction and working as a limiter.
How hard you can push the limiter depends on how well the track has been mixed before it hits the limiter. If it's not well balanced, like for example the kick is much too loud, it won't take long before the limiter "hits the wall" and the overall sound gets much too clippy/distorted/crunchy (whatever term you use). So you'll end up with this distorted track which still doesn't sound anywhere near as loud as your favourite tracks (if your favourite tracks happen to be loud). It's easy to hear the effects of over-limiting - just take the threshold way down and listen to the crunchy distorted mess. You don't want any of that in your track. If the crunchy sections are extremely short (a few ms) then the listener won't notice them.
To sum up: If you want hot levels, get the mix nicely balanced before it hits the limiter. To do that, it can help to either reference against your favourite tracks by ear, paying attention to where the lows, mids and highs are, or reference against them by using a frequency analyser, either in real-time or in a program such as wavelab or soundforge (I'm sure there are excellent freeware alternatives as well). See where a bunch of your favourite tracks are at (I'd suggest using a range of artists, rather than one, unless you're trying to sound exactly the same as another artist), then see where your tracks are in comparison. I generally use clips of the hottest sections of each track, maybe 15-30 seconds, long enough for the full melody to play once through.
edit: to briefly answer your question about what the limiter is doing - well, essentially, if you drive them hard enough, it'll turn your wave forms into clipped square waves - check out some loud wave forms, you'll see positive and negative sections of the waveform, which correspond to whether the sound is pushing or pulling air as it travels. At the top of the waveforms you may sometimes notice that the top of the waveform has been chopped off - it's square, it has hit digital zero. As I stated before, if this square, chopped-off waveform only lasts a few milliseconds, then the listener won't notice that the waveform has been chopped off. But drive a limiter too hard and you'll get heaps of these waves being driven into digital zero and ending up as square waves, and that will sound horrible indeed. But you can use your ears to tell you whether or not your sound is being adversely affected. if you can drive it loud without digital crunchiness, good. If not, work on your mix.
(Obviously, how loud you can make a track also depends on what style you're working on - you can't make a trance track as loud as a pop song because trance has these big kicks eating up a heap of headroom - if you tried to compete with a pop track your kick would become very small and non-trancey)
Last edited by derail on Mar-04-2008 at 03:09
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