Relationship between RMS and peak level

Sorry - newbie here and trying to get my tracks to meet ACX requirements - used the plugin and it works fine but I fail to meet the ACX requirements as my RMS value is wrong. Can’t find how to change it!! help would be gratefully received.

HI - been reading avidly here and learnt a great deal as I’ve decided to narrate and produce my own books - I had a publisher for my first one but did the narration - he got the files to ACX standard but I pay for the privilege. I’ve downloaded the ACX analyser and it works fine. I’ve worked out how to get lovely silence between phrases and pass the -60db check but can’t work out how to get the rms between 18 and 23db and keep the peaks below -3db.
I’ve tried changing the microphone level and can get the rms fine but then if I say a word even slightly too loud I exceed the peak even if its only occasionally. I can adjust the amplification or normalisation to keep a peak of -3 but then the rms goes out or I can get the rms in but the peak goes out as there seems to be a fixed relationship between them. Is there any way to get both within limits???
In anticipation.

Please don’t post the same question in different topics. I merged the topics for you.

Sorry am I being really stupid? - I can do what the other poster asked and adjust the volume - what I can’t do is then get the peak value back down.

Ah sorry - m y post got crossed because one took longer to moderate than the other and I thought it had disappeared.

The usual problem is that when the peak level is -3 dB (ACX requirement), the RMS level is a bit too low. Is that your problem?
If so, how much too low is it?

With the one of my basic tracks I have a peak of -4.3 and a rms of -30 if I normalise the peak to -3 the rms goes to 28.8. Some of the others aren’t quite so extreme but the same applies if I normalise the peak I still have an rms above 23. Why can’t I disconnect the two?

That’s pretty common. Are you using “acx-check?” Is that the software you said you had at the top of the thread? There is a technique to manually read all three ACX specifications on your work, but it’s pretty painful and time consuming. ACX Check gives you the whole pile in one swipe.

My experience has been to slide a pass of compressor in your processing path. Compressor’s job is to boost low volume without affecting high volume.

Audio Compressor
– Select the whole clip or show by clicking just above MUTE.
– Effect > Normalize: [X]Remove DC, [X]Normalize to -3.2 > OK
– Effect > Compressor: Thresh -20, Floor -40, Ratio 2:1, Attack 0.2, Release 1.0, > OK
– Effect > Normalize: [X]Remove DC, [X]Normalize to -3.2 > OK

That will give you the -3 for show peaks, it will give you a higher RMS (Loudness) and it will affect noise. It’s always a juggling act between the two loudness values and noise. If your RMS is not loud enough, run that whole process again on the original show and increase the Ratio from 2:1 to 2.5:1 or even 3:1. Everything else stays the same.

Normalize is set to 3.2 instead of 3 to guard against the MP3 process pushing you over by accident. The specification is just not go over 3.0 in the deliverable.

See how you do.


If you’re feeling adventurous, record a test sound clip according to this recipe …

… and post it here. We’ll see if your processing list matches ours. Do Not Process It. Raw recording only.


Koz - you’re a star - and saved me tons of work re-recording - that worked fine. I am using the ACX check diagnosis package and can now get on with recording. Many thanks. (mind you I haven’t a clue why it works but who cares!)


So - a happy day recording and saving then normalising to get ACX check to give the seal of approval. I also experimented with microphone record levels to get good sound - great. Er then I saved 6 chapters as MP3s and when I re-imported them the peak and rms values had shifted. I am now exporting as ‘WAV (microsoft) signed 16 bit PCM’ which seems to give a stable re-import So question - what is the best export file type to use and also use to upload to ACX in due course. I thought KDP and CreateSpace were difficult - wrong!!