Interpreting ACX-Check values

Audacity Help Forum Windows
1

Audacity 2.3.3 on Win 7 x64 SP1

I’m trying to interpret what ACX-check reports for my recorded audio clip.

  1. I don’t quite understand what the “A” letter is after RMS(A) is it absolute? or AC?
  2. The Noise floor values reported by ACX-check are -72.5 db, but when I select a section of the clip where there is not audio and just silence, I see the meters shuffling around -55db to -50db. So I’m a bit confused here how is -72.5 calculated when the meters show some other values?
  3. It says RMS level is outside ACX specification? are -18 to -23dB the recommended levels that should be shown on the meter while am recording?

Thanks in advance!
ACX-Check-Values.png

2

First, your levels are way too low!

When you amplify to bring your RMS level into spec your noise will be out of spec. (Your peaks will also be too high, but that can be fixed.)

[u]Recommended Audiobook Mastering Process[/u]

  1. I don’t quite understand what the “A” letter is after RMS(A) is it absolute? or AC?

It’s not part of the spec. It’s [u]A-weighting[/u] which corresponds to the ear’s frequency sensitivity so it corresponds better to how loud it actually sounds. SPL meters (loudness meters) are usually A-weighted.

  1. The Noise floor values reported by ACX-check are -72.5 db, but when I select a section of the clip where there is not audio and just silence, I see the meters shuffling around -55db to -50db. So I’m a bit confused here how is -72.5 calculated when the meters show some other values?

ACX found a quieter section.

  1. It says RMS level is outside ACX specification? are -18 to -23dB the recommended levels that should be shown on the meter while am recording?

No. Your meters show the peak level which is higher than RMS.

[u]RMS[/u] is a kind of average that correlates with perceived loudness better than peak levels.

Digital levels are not that critical as long as you avoid clipping (“trying” to go over 0dB). Most people shoot-for about -6dB on the peaks. But, it is important to get strong acoustic & analog levels for a good signal-to-noise ratio. (i.e. You need to speak with a strong-voice fairly close to the microphone.)

3

Thanks, Thanks and Many Thanks DVDDoug,

That just about sorts it all. Thank you for your time in answering this so elaborately.

For the whole story, I have been trying to get some decent output with the Zoom H5 with the XY microphone attachment. Due to recording while taking a video I have to keep the microphone a significant distance away from the source subject, about 3 to 3.5 feet away.
I hear a lot of hiss in the background of my recordings, the meters show me hiss levels of round -50db, and when the subject is speaking the levels go upto -20dB so that’s -30dB of signal to noise.
The gain levels were around 6 for the zoom h5.

I’ve heard that the noise levels should be -60dB or lower. I’m really struggling to get decent sounding audio.