There is only one current working ACX-Check. It’s by Steve Daulton based on work by Will McCown.
You don’t have to use it, but checking your work for Audiobook Conformance without it, while possible, is just not fun. You can’t do it just by looking at the blue waves. This is the process.
https://www.kozco.com/tech/audacity/ACXTesting/ACXTesting.html
Since audiobook reading was getting more and more popular, it was determined that designing a one-pass, dedicated test was desirable.
the modulation of my voice varies a lot more than it did in that small 10-second clip sample I sent to you.
Right. That’s a hardware error. The first thing the recording engineers do in their studio is clap broad, fuzzy headphones on your head so you can hear yourself.

That greatly reduces theatrical voice volume wandering. It’s nice to think you can solve all of these problems by pushing a button or applying a correction or effect later, but the headphone trick is a lot faster and more efficient.
This must be done by plugging your wired headphones into the microphone, interface, or sound mixer.

No we don’t recommend Apple earbuds for theatrical recording. They were handy for the picture. You can’t listen to the computer without reverb and echoes, so that lets wireless out.
The other trick to this is watching your recording levels which is what the recording engineer would be doing behind the glass wall.
This, in general, is what good recording volume should look like. We call for occasional sound peaks at about -6dB on the bouncing sound meter or about 50% height on the blue waves.
Yes, it’s good to keep one eye on the volume meters while you read. That’s what the recording engineer would be doing while the performance artist performs.
Another way to insure even, graceful reading is to not stop. If you make a fluff, pause really briefly, read it again—correctly—and just keep going. Some performers clap loudly once so they can find the error later by looking at the lumps in the blue waves. If you find yourself constantly doing that, then you may be reading too fast or the wrong person is reading.
If you find ticks or pops in your performance for No Good Reason, that can be a computer hardware problem that needs to be investigated.
One not very popular universal solution to a lot of recording problems is stop recording on the computer. That’s my Zoom H1n audio recorder.

Koz