Testing Noise Floor for ACX

I’m trying to test if I have the right set up for ACX(after recording for the much less rigorous Librivox) and can’t understand how to test the Noise floor on audacity 2.1.2, Mac. I saw some advice on a similar question that going to Amplify would give me the noise floor (I have 50) but I don’t understand how this translates into ACX requirements(-60db).

Also, how do I check that the audio measures between -23dB and -18dB RMS and has -3dB peak values ? Is this also related to the noise floor?

Many thanks


There is a plugin for Audacity which measures the ACX parameters, see …

How to install a plugin … http://wiki.audacityteam.org/wiki/Download_Nyquist_Plug-ins#install

That’s one in a series of tools and processes we wrote for Audiobook Production.


There is an error since the release of Audacity 2.2.0. You can’t select the whole track by clicking above MUTE. That graphic doesn’t exist any more. You click on the little blank spot in the lower right of the track INFO panel.

If you have reasonable recording hygiene, it should be possible to record a chapter, run it through those tools (in order) and out the door. The most likely thing to fail by far is noise. That’s why it has its own document.

Just for grins, record a test track and submit it to the forum. We will run it through the tools and see what’s what.



To specifically answer you, the classic way to measure noise before all the fancy-pants tools was with Contrast.

Drag-select a portion of noise-only performance. Analyze > Contrast > Measure Selection (write it down) > Close.

I wrote up all the older things you needed to do to prove ACX compliance and it was pretty grim. Flynwill wrote ACX-Check as an integrated collection of several existing tools. Much better.

One note: ACX would just as soon you submitted in Mono. All the tools and processes work better in mono too. Some of microphone systems don’t work in mono and you have to deal with that.


Thank-you very much for the replies.

1)I’ve tried several times (and re-read the how to install instructions) but can’t manage to install the ACX nyquist plug-in :blush: . It pops up as text and I can’t find the audacity library to send it to. It isn’t on the list of existing plug ins either. Can some-one please tell me what I’m missing?

2) In the mean-time I would love feedback on this test(attached).

I think I’m going to lock this thread. I’m answering almost identical questions over on your other posting.