On my current audiobook project, I have come across the issue of discrepancy between my recording (chapter) being passable on my ACX Check (plugin) but than it not passing on Audio Lab. I am using Audacity 3.7.5.
ACX Check Plugin Results:
Peak level: -4.48 dB Pass
RMS level: -18.93 dB Pass
Noise floor: -70.08 dB Pass
VS.
Audio Lab Results:
RMS is too low -24.4. Raise the level of this file by 1.4 dB.
But when I raise the recording by 1.4 dB, it no longer passes the ACX Check. The RMS, instead, is too loud at -17.53 dB.
What do I do, please? Will ACX accept the MP3 recording if it now fails the ACX Check at an RMS level of -17.53 dB?
There’s more than one way to calculate RMS (1) and I think ACX keeps their details secret so it’s probably best to trust Audio Lab. If ACX check is too close to the limits you might fail.
The peak readings are simpler and they should match, but there is also more than one way to measure noise.
Boosting by 1.4dB should increase the Audio Lab reading to -22.7dB and I assume that will pass. But it will make your peaks very close to the -3dB limit.
Or, the Audiobook Mastering Macro has some “wiggle room”, putting you in the middle of the RMS spec and leaving some headroom in the peaks so it should work every time.
(1) I believe it’s impossible, or at lease impractical, to calculate RMS for the whole file so it’s time-windowed and it’s an average of RMS calculations or an RMS of RMS.
Still, you can infer their goals. Play an audiobook into your earbuds and not have the volume wander.
Audio Lab is a relatively recent addition. They used to just let you guess at it. Lots of complaints about that.
That snaps us back to their desire that you create the book in manageable chapters. There is no measure the whole book at once (that I know of).
The Macro has some tricks. It applies the broadcast 100Hz rumble filter to keep thunder and earthquakes from affecting the work, and yes, it cheats a bit. It sets Loudness a little off, so that when it sets Peaks, everything comes out right. We will also note that when it sets Loudness, the peaks may exceed 100%. Audacity doesn’t care about that —it doesn’t clip—and everything just sails right along.
This is why it is strongly recommended that you don’t take the Macro apart and mess with the values. The tools talk to each other.
As it says in the notes, Audiobook Mastering Macro is not the current version. Right after I finished and published the original Macro, the company changed the tools around so it didn’t work any more. !@#$.
36Audiobook-Mastering-Macro.txt is the current working version.
I shot a test performance, cut out the mistakes, applied the latest Macro, and applied a very gentle Noise Reduction of the Beast (6, 6, 6).
I ran ACX-Test.
I got passing Peaks at 4.24 and AudioLab got 4.2.
I got passing RMS at 20.77 and AudioLab got 20.8
AudioLab doesn’t test noise. I got passing 67.92. I use 65 as my goal. Not 60.
I submitted as an MP3 and was surprised that AudioLab tested the technical compression quality at 192-Constant. Exactly what I used.
I would try sliding 36Audiobook-Mastering-Macro.txt in there and see how it works. If you have any rumble, sub-audible thumping , or microphone noise in the performance, that will very seriously throw off the readings.
Oh and one other oddity with the Macro. With one very minor exception, if you apply it and it’s not needed, it doesn’t do anything (I would limit my excursions to two).
I tried to find my local copy of 36Audiobook-Mastering-Macro.txt but I can’t. I’m on a new machine because Audacity has seen fit to lock my older machine out of the forum. I more or less know where the macro is on-line, but I don’t remember how to copy and paste forum postings into each other.
And something I ran to almost immediately, Macros are dead simple text files. That means every application ever written thinks it is its duty to muck with it. The official Macro file has dot-t-x-t at the end. If yours doesn’t have that, it means your computer is conveniently hiding it “to help you.”
Since it is a plain text file, you can open it up in a text editor (I use TextEdit—set to plain text—on my Mac) and read it. The first line is comment.
Comment:_=“36Audiobook-Mastering-Macro.txt runs the ACX Audiobook Mastering Suite in Audacity 3.6x 20240730 Kozikowski”
It’s also sightly wrong. It runs in 3.6 and later.