Peak vs RMS compression: The difference between Peak and RMS

In this article, we’ll look at peak vs RMS compression detection modes. With modern day compression plugins, its not uncommon to have a ‘Peak’ or ‘RMS’ option. A compressor can function using either peak sensing or RMS sensing. Each mode means that the compressor will react slightly differently to signals that overshoot the compressor’s threshold.

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What is Peak compression?

In peak mode, the compressor will respond to the peaks in an audio signal. As such, any peak that overshoots the threshold will be compressed.

What is RMS compression?

RMS, which stands for root mean squared, works a little differently. The RMS mode responds to the average loudness of a signal. Accordingly, occasional peaks in your audio signal may overshoot the threshold without being compressed. The compressor will only attenuate the signal when the incoming signal’s average level will be above the threshold for a sustained period.

How Peak vs RMS compression modes work on your plugins

With modern day plugins, some work only in peak mode while others work only in RMS mode. With some compressors, you have the option to toggle between the two. There are also compressors which allow you to dial in your own setting by telling the compressor the time period over which level changes should be measured. In this instance, a short time period would represent peak sensing. Increasing the time period would change the compressor’s mode to RMS sensing and the average level of the signal would be measured over the time period that you have specified.

When to use Peak vs RMS compression

If your compressor allows you to select between Peak and RMS sensing, then you could try using peak sensing on things like drums to make sure that your compressor catches all of the short sharp transients of the kick and snare. Then you could try using RMS sensing on things like vocals which tend to rise and fall in level over more sustained periods.

That said, there’s no reason that you can’t use peak sensing for things like vocals too. In fact, in the days of analogue recording, the vast majority of hardware compressors functioned in peak mode. The reason to experiment with RMS mode however, is that the compression tends to be more subtle than it is in peak mode. As such, RMS can often be utilized to create more natural and transparent level attenuation. Of course, the trade off is that, not everything that overshoots the threshold will necessarily be compressed in RMS mode.

Do you switch between Peak and RMS mode on your compressor? If so, which mode do you use for different instruments?