RMS Normalize

This effect “normalizes” the selected audio to a specified RMS level.

This effect does not change the dynamics, it only changes the overall level.

Possible uses:

Recordings for commercial use (such as audiobooks) are frequently required to meet a specified “dB RMS” range. For example, the requirement specified by ACX / Amazon audiobooks is -23 to -18 dB rms.

The RMS level is a better approximation of “loudness” than the peak level, so this effect may be useful for amplifying tracks / audio clips to approximately the same level (though the ReplayGain plug-in may be better for this purpose).


This effect may be used on mono or stereo tracks up to 200 million samples duration (about 1 hour 15 minutes at 44100 Hz sample rate - see warning below).

The RMS for stereo tracks is calculated as the “square root of (the average of the squared amplitude for both tracks)”. Reference: http://replaygain.hydrogenaud.io/proposal/rms_energy.html

Expected accuracy is within 0.1 dB.


Like many Nyquist Plug-ins, the maximum selection is limited by available ram (up to a maximum of 2 GB). The selection length is therefore limited to 200,000,000 samples (about 1 hour 15 minutes for a 44100 Hz sample rate track. An error message is returned if the selection is longer than 200 million samples. If you wish to apply this effect to very long recordings, it may be applied to sections of less than 1 hour.

On long selections the effect is slow, taking several minutes to process a 1 hour track.


If the computer has less than 2 GB of physical ram free, Audacity will crash if the selection is larger than the available ram.

The RMS level of a signal is always* lower than the peak level, so to avoid clipping the normalization level must be substantially less than 0 dB. The default is -20 dB, which should be safe for most recordings.
(* Except for square waves, where the peak level and RMS level are the same)

Installation instructions:

rmsnormalize.ny (2.51 KB)
UPDATE: For Audacity 2.1.3 or later, use the updated version here: https://forum.audacityteam.org/viewtopic.php?p=325078#p325078

How close is Make-ACX? Apply all the filters and corrections needed to force a submission into ACX Compliance.


I think that we’ve got most of the components now haven’t we?

  • DC Offset removal: check
  • Rumble filter: check
  • Noise Reduction: check
  • Compression: check
  • Equalization: check
  • Low distortion peak limiter: check
  • RMS Normalize: check
  • ACX Compliance test: check
  • A good clean recording so that the above are virtually unnecessary: Ahh… I can’t do that with a plug-in.

[_] Completely automated.


I think it was Beethoven: There’s all the black and white keys. What’s the problem?


Sounds like a job for your PAF effect.

Sounds like a job for your PAF effect.

Yes, or the follow-on tool CleanUp®.

It’s been my experience that many people start with my personal recommendation of Normalizing the peaks to 3.2dB and then find that the RMS level is too low. That’s endemic bordering on epidemic. Given RMS Normalize will refuse to cause peak sound damage, aren’t we at the same point?

Oops. Sorry. Time for other, more serious processing tools.

Even worse, if RMS Normalize borderline succeeds, couldn’t that leave peaks at some very high value, say -0.5dB? Fix the peaks and the RMS value dies—assuming no compression.

I’ve never experienced, including my own test recordings, dense vocal work where RMS is set and the peaks naturally fall below the high limit. Taking that upside down, I’ve never experienced Normalizing to 3.2dB and had a performance RMS too high. People who can do that are vocal or performance celebrities, not the AudioBook reader next door.

I kept coming back to setting peak first and then help the performance along if needed. The last voice test I did only Normalized peaks to -3.2dB and out the door.

As close to PAF as you can get.


I downloaded the rmsnormalize.ny plug-in and placed in the plug-ins folder within the Audacity folder in the Program Files directory. However, it does not show up in the Effect menu when I open the Audacity application.

Which version of Windows?
Which version of Audacity? (look in “Help > About Audacity”)

I have the same problem, I’ve downloaded it and put it in file but it’s not showing up under Effects. (I don’t understand the advice to check Help under Audacity, there’s nothing there about this I can spot).

Anybody know how I can get thae plug in to show up in my Effects menu? I’m using Windows 10. Thanks!

Assuming that you are using the current 2.2.2 version of Audacity, see here for how to enable plug-ins: https://manual.audacityteam.org/man/manage_effects_generators_and_analyzers.html

DC Offset removal: check
Rumble filter: check
Noise Reduction: check
Compression: check

And right there is a problem. There’s a reason Limiter follows RMS-Normalize in Mastering 4. RMS-Normalize is a volume defining tool. Limiter isn’t.

The first three tools don’t care at all the volume of the original. Compression does. Compression works from a known good volume. It’s not open ended. You need a volume definition step before compression in order for it to do predictable things.

Compression: check
Equalization: check

Those are performer dependent. How much equalization is my voice going to need?

I think it’s a mistake to combine theatrical sound quality corrections in the same tool as “make it past ACX Check.”

It’s a goal of Mastering 4 to have the tools not do anything if they’re not needed.

I can imagine automating Mastering 4 and applying it twice. Once to get the performance in the ballpark enough to apply performance dependent corrections (de-essing, de-clicking equalization, compression), and then again just before submission.

Somewhere in the middle you find out your apartment is too noisy and so starts the multi-month quest to meet ACX Noise in addition to the other two.

If this was easy, anybody could do it.