I am often asked what is the difference between a limiter and brickwall limiter and when would you choose one over the other. To answer this question we need to first look at how a limiter works:
A limiter keeps signal peaks from exceeding a pre-determined level.
While a compressor reduces the overall dynamic range, a limiter affects only the highest peaks. Limiters have very fast attack times, very high compression ratios and a high threshold. You can turn your compressor into a limiter by using a very high threshold and ratio.The ‘classic’ definition is that a limiter ‘flattens’ all peaks above a certain level, but leaves lower-level sounds intact. This sounds unnervingly like a compressor but there is a difference in how the threshold is defined between the two topologies. In traditional downward compression the threshold is used to determine at which point compression take place. Everything above the threshold is compressed whereas everything below the threshold is left untouched. With limiting the threshold is used as an output ceiling in that the ceiling sets the maximum output value that the limiter can then drive into – in other words the signal is not allowed to exceed the threshold. We use the term ‘ceiling’ to describe this type of threshold. We vary the gain of the input signal to force it into the ceiling. The more we drive the input into the ceiling the more limiting effect we achieve. Limiters are great for capturing peak transients, ISPs (intersample peaks) and errant spikes. The fast attack ensures that transients are captured immediately and the high ratio allows for a fast gain reduction of peak transients.
Now that we understand what a limiter is and how it works we can look at brickwall limiting.
Whereas a traditional limiter will allow certain peak transients to exceed the ceiling when the input gain is driven hard a brickwall limiter will not allow any transients, be they ISPs or random errant spikes, through irrespective of how hard the input is driven. For this reason alone mastering engineers use brickwall limiters to catch any ‘overs’ that have been missed through the signal path. Nowadays we use brickwall limiters on the master bus of the DAW to capture all errant spikes and we do this specifically when using LUFS metering that allows for true peak metering. Traditional PPMs didn’t allow for monitoring ISPs and were therefore not true peak meters. This meant that errant spikes would come through undetected.
In the video I explain how to use a brickwall limiter to limit a stereo mix. I show you how to use metering to ascertain how the limiter behaves and I explain how the different parameters of a brickwall limiter affect the overall result. I show you which settings to use and why and end by running the mix through different limiter topologies.
Plugins used in this video:
Topics covered in this video are:
- The concept of Brickwall Limiting
- Functions and Usage
- Understanding Ceiling and Headroom
- Mixing the Formats