Transparent Limiting with a Compressor

How to use a compressor as a transparent Limiter for pre-mastering your mixes.

Compression


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In modern day productions limiters are used not just to capture peak transients but as colouring processors. The topology (design) of a limiter usually determines how the process is executed but we are starting to see limiters being used purely for colour and not just for managing peak transients. Minimum phase designed limiters impart a certain colour/texture onto the audio being treated and this is what makes this type of design so attractive to producers and mastering engineers but they can also behave transparently if used correctly.

This tutorial concentrates on using a minimum phase designed compressor as a limiter and to limit a stereo mix transparently.

If you are confused about the differences between minimum and linear phase please watch this tutorial: Phase – what is total and partial phase cancellation

Limiter

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.

Although limiters were exclusively used for managing and controlling peak transients producers nowadays use them to colour the signal path and we are now blessed with many reincarnations of iconic classic limiter topologies. However, we still use limiters to grab errant spikes and manage the overall gain of the signal and for that we need to look at transparent limiting.

In the video I use a minimum phase designed limiter and show you how to use it transparently to limit stereo mixes. I use the wonderful Acustica Audio Pink channel strip and show you how to use it transparently on a stereo mix. I show you how to match the input signal against the output signal to achieve unity gain. I explain how to structure the Pink compressor to behave as a limiter and show you how to edit the parameters to achieve a transparent texture.

Plugins used in this video:

Sonarworks Reference

Acustica Audio Pink

Topics covered in this video are:

  • How to use a Compressor as a Transparent Limiter for Pre Mastering
  • Signal Path Management
  • Minimum Phase – Linear Phase
  • Pre to Comp, before or after
  • Working Ranges and Responses