installing NYquist plugin RMS Normaliser

macOS Catalina V 10.15.7, on a Macbook Pro (mid2012), using Audacity 2.3.1

I’m creating an audiobook, and the publisher’s requirement is that “Each file must measure between -18 and -23dB RMS”

I’m struggling to get this to happen. Having recorded the entire book as one file on Garageband, using the ‘natural voice’ presets, which gives a gorgeous sound quality, I exported the file to mp3 so that I could easily edit the fine details in Audacity. (I can record on Garageband, but anything else there is beyond me, after 20 years of various attempts to get to grips with it)

In Audacity I created individual files for all the chapters etc, and exported these as mp3s. These have been rejected by the publisher, who says they are outside of these limits.

I installed the "Measure RMS " plugin, which reveals the individual files have all ended up with different RMS, some outside of these limits.

So I downloaded the Nyquist plugin RMS Normaliser, and placed it in the plugin folder, but it does not show up in the programme. I have closed and re-opened Audacity, still no sign of it. Also, "Show ALL’ is enabled.

There is one called “Nyquist Prompt”, which I’ve experimented with. It allowed me to find RMS Normaliser, entered its code and submitted it. No change that I can see.

I’d be most grateful for any advice. I’ve read and re-read the manual instructions for installing Nyquist plugins. I have downloaded the Nyquist installer, it is not appearing anywhere. I suspect it is actually what is now called Nyquist Prompt. But is it? It’s a mystery.

All I want is to have my files accord with the publisher’s requirements. Any help would be so welcome. Urgently. ( and yes, I know, my machine is now a Vintage model)

The Nyquist plugin RMS Normaliser is effectively obsolete now that Audacity has a “Loudness Normalization” effect:

The Loudness Normalization effect is included in Audacity 2.4.2 which is available via the Audacity website:

Also, if you aren’t aware already, a lot of people use audacity for audiobook mastering. Please read Audiobook Mastering at