RMS levels in mastering (with free Vst metering tool)

Hello everyone and welcome to this week's article!
Today we are going about Mastering, and in particular of RMS levels when using the last plugin of our chain in the stereo bus: the limiter.

As we know, a limiter is a tool that prevents any peak to surpass a certain ceiling, and does this by applying a strong gain reduction that blocks the loudest part of the signal.
We have also already talked about the Loudness war so I won't repeat myself here, what I think is an interesting addition is though the reading of the RMS meter.
In order to introduce this concept we need to explain the difference between Peak Level and Rms Level.

Peak level: this is the loudest peak reached by our track. When mixing it could be -12db, but when mastering we can use a Limiter and stop it at -1db, or -0,1db.

Rms level: root means square level. This level is the AVERAGE loudness of the master, and the difference between the peak level and the rms level is an approximation of the amount of headroom left in our master.

What is a good compromise between a mix that is loud enough and that is not squashed?
A good starting point is to limit not more than 3/4db of peak, but keeping ourself at around -9/10db Rms.

In this interesting article Ian Shepherd on his mastering blog compares several recordings, showing the average (raw) rms levels:

-6.2 Oasis - "Some Might Say": Severe clipping distortion
-4.9 Metallica - "The day that never comes" (CD): Massive distortion & clipping
-7.7 Feeder - "Pushing The Senses": Heavy clipping distortion
-10 Katatonia - "Consternation": Awesome (clean) sound, massive choruses
-13.1 Sugar - "Fortune Teller": From 1993
-16.9 Metallica - "The day that never comes" (Guitar hero 3) Needs to be louder !
How do we measure the Rms level? A good free tool to monitor our Rms level is Sonalksis Free G, which offers a master fader and a serie of metering tools (place it after the limiter in the post-fader insert).

And you? What Rms level do you like to master your music? Let us know!


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