I've done - you've done it - we've all done it. You see the waveform of a piece of music slamming up to zero dB, you can see it's had a brickwall limiter slapped across it in mastering, and you assume it's going to sound like crap.
And sometimes you'd be right.
But not always !
In fact, there are many misconceptions about limiting, especially since the Loudness Wars have been getting more press, and too many people seem to have decided that limiters are actually evil - by definition.
Whereas in fact, when I started my career as a mastering engineer over 15 years ago, I often used only EQ and a limiter on most mastering projects as a matter of course.
Why ? Because the simple truth is:
A limiter is the most transparent way
to boost average level without clipping
Hang on, I haven't finished yet -
...provided you don't overdo it.
Because people don't understand how to use them. The flawed reasoning is:
Before we look at the problems with this in more detail, we need to make sure we're on the same page. I want my mastering limiters to be "transparent" - but what does that mean ?
When I say "transparent", I mean "invisible".
So to me, a "transparent" limiter allows me to lift the average level and prevent clipping, without hearing any adverse effects - any distortion, pumping or loss of impact. In the same way, a transparent converter won't colour the sound in any way going from analogue to digital or vice versa, and a transparent window lets the light through without tinting it.
So now we get to Important Statement Number 2:
Any limiter will damage the sound if you push it too hard
And that, in my opinion, is where the bad reputation of The Limiter stems from.
People push them too far.
A great limiter can invisibly shave off several dB from the waveform of a mix without any audible side effects, especially if the original is good and dynamic (has a decent peak-to-loudness ratio) to begin with. That's because transients happen so quickly our ear barely registers them anyway.
But as soon as a limiter starts to cut into the body of the sound - meaning anything that lasts more that a fraction of a second - it's effects start to become highly audible, and usually undesirable.
(I'm talking about mastering limiters, not limiters used creatively in a mix, by the way.)
And any compressor with a ratio higher than 8:1 is approaching limiting!
As part of a mix, the aggressive gain reduction of a limiter might be exactly the sound you're looking for. But in mastering, transparent control is the goal, usually. (Some people come to me wanting something more characterful, but personally I think it's better to get it right at the mixing stage if possible.)
So what's the solution to this ?
Pushing a limiter too hard can cause a variety of unpleasant effects on the audio:
(This is precisely because of the same characteristics that make them very transparent when used more conservatively - namely very high ratios & fast attack and release times.)
However what does work well is to use a compressor followed by a limiter.
Since the limiter will protect you against any clipping distortion, you can use slower, more natural-sounding attack times on the compressor to keep the punch and impact of the mix. These won't catch the fast transients but will control the "body" of the sound more gently and effectively. Then the limiter can work much less hard and control all the fast transient detail - invisibly.
If you want to go a step beyond this, you could consider using multiband compression. This can be a great technique to get high levels without crushing - pulling a mix together while keeping all the punch, power and air.
And if you'd like to see some of the ideas in this post in action, click here:
How to master a song loud – and the price you pay (Video)
Original image by Grant MacDonald
